Sekaiichi Hatsukoi Episode 0.

Onodera begins work at his new position at Emerald, and is harshly introduced to their production "cycle" by being thrown into the mess of their burned-out phase, in which everyone appears brutally overworked and exhausted. He is shocked to find them transformed the next day into composed and energetic people who spiritedly show him the basics of manga editing.

As Onodera continues learning the ropes of manga editing and publishing, his interactions with Takano become more tense and uncomfortable. Takano eventually realizes who Onodera is, later revealing his identity to Onodera as his first love from high school, bringing back memories of being used and tossed aside, even though, as Takano explains, they were fuelled by a gross misunderstanding. He is left conflicted in regards to his true feelings toward Takano.

After Takano and another staff member have a heated argument in the Emerald office about an underprinted publication, Onodera sees the two of them later having a seemingly friendly conversation in the lobby, stirring a sense of jealousy within him. Perturbed by the fact that this bothered him, he begins avoiding Takano even more, prompting Takano to confront him about the situation before it begins affecting their capacity to work together.

The author that Onodera has been overseeing suddenly falls ill along with all of her helpers near the publication deadline. He rushes to the distant Hokkaido to assist her personally, despite protests from his superiors. As the entire editing staff stands on the end of their nerves, Onodera barely makes the deadline with the finished manuscript. He later falls asleep on the train with Takano, and finds himself sleeping in the same bed as Takano the following morning, flustering his emotions and pushing him further into refusal to open himself to Takano.

This episode introduces a new set of characters - Chiaki Yoshino, a male author who releases shōjo manga under the female pseudonym Chiharu Yoshikawa; Yoshiyuki Hatori, his manager and childhood friend; and Yuu Yanase, his chief assistant, who is on rough but unclear terms with his manager. Hatori's increasing coldness toward Chiaki begins to take its toll on their friendship, and when pressed on personal matters, Hatori becomes distant. Chiaki later sees Hatori and Yuu in an alley having what he interprets as an argument between lovers. Growing distraught with confusion that begins to affect his ability to write, Chiaki slowly realizes his feelings for Hatori. However, Hatori later confesses his love for Chiaki, much to his surprise, along with admitting that he had changed Chiaki's management behind Chiaki's back, fearing that his confession would put their relationship on bad terms. This forces Chiaki to admit his own budding feelings.

After an onsen trip, Chiaki is burned out and can hardly concentrate on work. The emerging love triangle between him, Hatori and Yuu compounds his inability to focus as well. Later on in Chiaki's apartment, Hatori informs him that he must attend an upcoming party because his manga will be made into an anime and he must meet the people in charge. Hatori offers to pick a suit for Chiaki, but Chiaki prefers to go shopping with Yuu instead, sparking jealousy in Hatori. After Yuu leaves, Hatori makes tries to kiss Chiaki, upon which Chiaki pushes Hatori away because he feels that Hatori is moving too fast. This upsets Hatori and he leaves. During the party, after meeting the anime staff, Chiaki sees Hatori surrounded by many women, including Ichinose Erika; a top writer who is known to have taken a liking to Hatori. Chiaki, feeling that Hatori is comfortable with the writer, becomes jealous and promptly leaves the party with Yuu. Hatori eventually arrives at Chiaki's place because he still needs to discuss some corrections with Chiaki's manga. Chiaki smells perfume on Hatori; feeling that the writer at the party may have gotten too close him, he becomes angry. Hatori reassures Chiaki otherwise and also confesses his jealousy about Chiaki and Yuu, feeling that Chiaki favors Yuu over him. Chiaki also reassures him and Hatori tells him that he loves him, and will continue to tell him until he can never forget. The morning after, Yuu admits to Chiaki that he is in love with someone, but when Chiaki asks who the person is, he simply says that Hatori knows the person well, leaving Chiaki puzzled and confused.

The episode begins with Ritsu having another flashback dream, in which he sees Saga sleeping in the library and tries to find out what book he was reading, but runs away when he thinks Saga is about to wake up. Afterwards, Ritsu wakes up and goes to work. At Marukawa, Ritsu's assignment is to make his first proposal as a manga editor to publish the manga he's supervising as a book. It is initially rejected by Takano, so he stays late at night working on it. Later that night, Takano helps Ritsu with his proposal, even though Ritsu didn't want his help. After a while, Takano suddenly kisses him to break the tension, and consequently gets hit by Ritsu. Yokozawa then arrives and sends Takano to meet someone. When he's alone with Ritsu, Yokozawa proclaims Takano as his property, and doesn't believe Ritsu's words about not having any relation with Masamune other than that of boss-subordinate. At a bookstore the next day, Ritsu meets an old female friend from his previous job, and they go for drinks. She gets drunk, stumbles, and falls into Ritsu's arms. This is seen by Takano, who had just arrived with Ichinose Erika, a female writer, to discuss work (Ritsu misunderstands this and feels jealous). When he arrives home, Takano accuses him of not working hard enough. Takano makes another pass and admits to being in love with him, but Ritsu (who is still wary of admitting his love for Takano) runs away and leaves Takano alone in his apartment. The proposal meeting day arrives and Ritsu is quite nervous, but Takano tries to cheer him up on the way to the meeting. In this episode another Junjou Romantica character appears; Isaka Ryuichiro.

Kisa sees Yukina, the Marimo Books employee he has been attracted to for a long time, selling the latest book he has edited. Tall, handsome and charming; Yukina is extremely popular among girls, who are easily convinced to buy the books he is selling. Kisa does not believe they could ever be together. Checking the sales of his book, Kisa notices that the sales are very high at Marimo Books, as they have been for his previous books too. They are finally introduced to each other by Yokozawa in the bookstore. Just as Kisa is leaving the store, he runs into a persistent ex-lover. After being rejected yet again, the man is about to hit Kisa when he is stopped by Yukina, giving Kisa an opportunity to flee. Later on, Yukina happens to find Kisa in the little-known cafe he had run away to. They talk, and Yukina correctly guesses the authors Kisa has been in charge of, saying they had a similar atmosphere despite being very different books. He is also astounded by Kisa's youthful looks after learning he is actually 30 years old. Yukina reveals he himself is a 21-year-old art student. As he plans a fair to promote Kisa's latest book, it begins to rain. Kisa, however, is lost in thought and doesn't hear Yukina asking him if he has an umbrella. Noticing this, Yukina leans in and kisses Kisa.

Kisa freaks out and cannot concentrate on his work because of his constant flashback to the scene with Yukina at the cafe. He soon receives an e-mail from Yukina inviting him to the bookstore to see the book promotion display stand that they planned earlier. This reminds Kisa of the kiss and he throws himself into a brief depression after convincing himself that Yukina cannot be serious about the kiss. He gets even more down after belittling himself career-wise by comparing his achievements to Takano's. After work, Kisa subconsciously arrives at the bookstore, where Yukina shows him the display stand and tells him that the reason he worked so hard on the display was because of Kisa. Noticng that Kisa has been trying to avoid him, Yukina invites him to talk after he finishes work. As Kisa waits for Yukina outside the store, he encounters the persistent ex-lover yet again. The ex-lover finds out about Kisa's feelings for Yukina and threatens to expose him but was defeated by Yukina, who appeared suddenly and claimed himself to be Kisa's boyfriend. Kisa and Yukina end up in Yukina's house, where Yukina finds out that Kisa was in charge of editing all his favorite manga. He then surprises Kisa by telling him how he knows about Kisa's feelings for him from the start, but when he begins to talk about the kiss Kisa immediately interrupts him by saying that he does not care, which triggers an unexpected response from Yukina, who confessed his love for Kisa. Afterwards, Kisa receives notice that his book is getting a second printing, and when Yukina tells him that he loves him after Kisa notified Yukina of the news, Kisa decides that he has fallen in love despite the fact that he claims he can only like men's faces.

After working through the night to finish work, Yoshino and Yuu stays behind together. Yuu saves Yoshino from falling over the trash can, and starts to tease him by tickling him. Hatori walks in on the scene and misunderstands. Later, Yoshino arrives at Hatori's house and attempts to apologize, but gets mad at Hatori when Hatori says he does not want Yoshino to have physical contact with Yuu. They make up temporarily in the morning after Yoshino sleeps over, but gets into a dispute again when Yoshino reveals that he is going to a hot spring with Yuu. On the night of the hot spring trip, Yoshino is surprised to find out that it is his own birthday on that day and realizes why Hatori is upset about his going away. Briefly after his realization, he receives an unexpected love confession from Yuu, but is interrupted by a phone call from Hatori. After hearing a "Happy birthday" from Hatori through the phone, Yoshino suddenly decides to terminate the vacation and go back to Hatori's house, where Hatori gave himself to Yoshino as a birthday present.

Onodera wakes up in the doorway, still holding on to a convenience store-bought dinner, and suddenly remembers a meeting that he was to sit in in the morning. On the subway, he complains about his lifestyle after joining the shōjo manga department. Onodera is surprised by the hostility shown in the proposal meeting and dreads future meetings. After the conference, Onodera meets Sumi Ryouichi (father of Sumi Keiichi from Junjo Romantica), whom he was in charge of before in the literature department at his father's company. Through Sumi sensei, Onodera also meets Hasegawa of the literature department, who later dropped in on Onodera during work and invited him out for a drink. Takano, who happened to hear the invitation, rejected it for Onodera. After commenting on Takano's strictness, Hasegawa reminds Onodera that he can always transfer to the literature department if he no longer wants to work on manga. Later, Onodera encounters Takano at the library and tries to run away. Takano saves him from falling down the stairs as Onodera trips on fallen leaves; as they embrace on the stairs, Takano tries to evoke past memories from the time when they were dating in high school, but Onodera escapes again. At the apartment, Onodera encounters Yokozawa, who apparently was coming out from Takano's room with Takano's cat, Sorata. Yokozawa confronts Onodera and claims Takano as his, and further throws Onodera into confusion by recounting how Onodera had only hurt Takano since they have known each other.

Meeting Ryouichi Sumi and the advice from Hasegawa have put doubt into Ritsu Onodera's heart. He remembers the reason he transferred to Marukawa and wonders if he can continue to work as a manga editor. While he is struggling, Takano asks him if he wants transfer to the literature department. A call from an author interrupts Onodoera's thoughts, and the author expresses her gratitude for his work and gives him encouragement. Onodera relays her praise to Takano, who further shows his approval of Onodera's work. While at Onodera's place, Takano tells Onodera of the history between him and Yokozawa. As Onodera is immersed in his own thoughts about the two, Takano once again confesses his love for Onodera. This is the finale of season 1.

Hatori and Yoshino have been going out for a year now, and Hatori reflects over that. Yoshino gets a call from his mother who complains over how he never visits. As Hatori plans to go to his parents’ house, Yoshino decides to go along with him and visit his mother and sister. While there, Mrs Yoshino makes a remark how Hatori and Chinatsu (Yoshino's sister) would make a nice couple, which makes Yoshino jealous. Hatori is touched by how much Yoshino cares for him.

Onodera leaves the office to visit the bookstore and thinks about how it has felt whenever Takano has touched him, but he dismisses these thoughts. At the bookstore, he runs into Yokozawa, and as they leave together, Yokozawa demands that Onodera move to a new home. Onodera argues that it his none of his business and teases Yokozawa that maybe he and Takano were dating. Yokozawa confirms this suspicion and Onodera realizes that Yokozawa doesn’t like him because he is protecting Takano. Back at the office, Onodera overhears a conversation between two women, one of whom saw Takano and Yokozawa together the night before. Takano invites Onodera to dinner, and though Onodera declines, Takano makes the plan anyway. Onodera tries to avoid having dinner with Takano, but Takano catches him and they go to dinner at Takano’s apartment. At dinner, Onodera becomes intoxicated and drunkenly confesses that Takano’s behavior has an emotional effect on him. The next morning, Onodera awakens to find himself naked in Takano’s bed, unable to remember the events of the previous night, but pain in his hips and back leads him to realize that he and Takano had had sex. Despite this obvious evidence, he openly denies this taking place.

Onodera reflects upon how he imagined Christmas would be when he and Takano were together 10 years ago. Onodera runs a manuscript over to the printers and upon arriving back at the office, he receives an email from Takano telling him he can go home. As the elevator door opens, he sees Takano and Yokozawa talking and when the leave together, Yokozawa asks what Onodera’s plans are for the 24th, which happens to be Takano’s birthday. Yokozawa then implies to Onodera that he and Takano are still together, and he warns Onodera again to stay away from Takano. Onodera wishes Takano a happy birthday and as they part, Takano requests Onodera’s company on a drive for his birthday gift. On the drive, Onodera reflects on his feelings toward Takano, and Takano reveals the true nature of his relationship with Yokozawa and reminds Onodera that he has loved him for 10 years. They kiss, and Onodera admits to himself that he cannot resist Takano.

Yoshino is conflicted between his fondness for Hatori and his friendship with Yanase. Hatori makes a movie date with Yoshino but cancels at the last minute due to work. That same day, Yoshino becomes upset when he spots Hatori with an old high school girlfriend. While brooding over the incident, Hatori calls Yoshino, who hangs up on him. Yanase invites Yoshino to his house, where they recall Hatori's former girlfriend from high school and Yanase implies that Hatori is cheating on Yoshino. Hatori phones and Yanase tells him he intends to make Yoshino his boyfriend. ...

Onodera receives a call at work from An, a girl his parents arranged to be his fiancée, who wants to meet at his apartment that night to give him a New Year's present. Takano overhears the conversation and ask Onodera if she is his girlfriend, which he denies. Later, as they approach their apartment building they see An waiting for Onodera. Takano again asks if she is his girlfriend and An is taken aback when Onodera answers 'No'. After An departs, Onodera is concerned that Takano misunderstands his relationship with the girl and contrives a way into his apartment. ...

Marukawa Publishing executive Isaka Ryuichiro is in love with his assistant Asahina Kaoru. He recalls when they met as children, through the time when Isaka hoped to become a writer. One night Isaka suddenly kisses Asahina and his affections are rejected. Asahina quits Marukawa to become assistant to Isaka's father. When Isaka confronts Asahina about this, the latter confesses his love for Isaka, explaining he had earlier rejected him because he thought Isaka already knew of his love and was making sport of him. Shaken by the confession, Isaka wonders how they could ...

While preparing for the company's New Year's party, Onodera gets a call from his mother, who pesters him about his engagement to An and asks him to escort her from a wedding that coincidentally is taking place in the same hotel as the company event. At the party, Onodera encounters Yokozawa, who accuses him of slacking at work but Takano defends him. Onodera is surprised to find An waiting for him since he had told his mother he couldn't see her. An reiterates her love for him but Onodera tells her he can't love her the way she wants him to. An asks if he loves ...

As Yoshino struggles to meet a looming deadline, he wishes his assistant Yanase could help but doesn't ask, knowing Hatori despises him. Yanase appears of his own accord and helps finish the project but Yoshino collapses from overwork. On awakening, Hatori tells him he was rushed to the hospital and has slept for two days. After Yoshino recuperates, Yanase reveals he has romantic feelings for him. Just then, Hatori walks in and immediately exits. After not hearing from Hatori for a week, Yoshino arranges a meeting between them. When a gloomy Hatori says he expects ...

Kisa has the perfect boyfriend in Yukina but is riddled with doubts about their relationship. He is concerned his heavy work schedule prevents them from being together often and interprets Yukina's understanding of the situation as a sign of indifference. Kisa's fears are heightened when a colleague tells him she's getting married because a job can't provide the same stability as a relationship. When Kisa finally makes a date with Yukina, he's delayed because of a work commitment. When he calls to explain, Yukina suggests they put the date off and an angry Kisa hangs ...

Believing Yukina has cheated on him, Kisa becomes distracted at work and won't respond to Yukina's messages. Accidentally answering one of Yukina's calls, Kisa tells him their relationship is over. That night, Kisa reflects on Yukina and realizes he knows little about him as their time together was mostly spent having sex. Kisa receives a call from an old boyfriend and agrees to hook up with him since he's no longer seeing anyone. The man arrives and just as he and Kisa start to kiss, Yukina appears, slaps Kisa's face and tells the other man to leave. Inside Kisa's ...

Onodera enters the office elevator with Yokozawa and Takano, who he is coming down with a cold. Onodera is jealous when Yokozawa touches Takano to take his temperature. Takano corners Onodera in the lunch room and reminds him of what he told fiancée at the New Year's party. Onodera tells him he only told her he loves someone else due to circumstances. The next morning, Onodera hears that Takano is out of the office due to illness and he wonders if anyone is taking care of him. That night he brings medicine for Takano but Yokozawa answers the door and the two get into ...

Takano and Onodera share a moment in the rain and talk about their time in school. A few startling truths are revealed that may change their opinion about each other.

Takano remembers how he fell in love with Ritsu and his problems with his family. This is the season finale.