After just being dumped by her boyfriend, Yū's friend Misa Nakamura follows Koizumi to a ramen shop and ends up picking its spiciest dish, Hokkyoku ramen. Taking a liking to the extremely spicy ramen, Misa lets out her frustration over her breakup and becomes friends with Koizumi. Later, Yū's other friend, Jun Takahashi, is asked to speak with Koizumi about her poor test results, which turns out to be because she was exhausted following a ramen pilgrimage. Hearing about all the peculiar flavors of ramen Koizumi has tried, Jun decides to try out a Pineapple Shrimp Salt ramen at a local ramen shop, finding she still loves ramen despite how it fogs up her glasses.

As Yū tries to invite Koizumi to a WcDaniel's restaurant, Koizumi explains how she once had saimin noodle soup from a WcDaniel's branch in Hawaii. Later, Yū goes with Koizumi to a peculiar restaurant where customers eat in secluded cubicles and order using forms. After finding Koizumi collapsed from starvation due to her favorite restaurant being closed, Yū takes her back to her house and makes her various homemade ramen dishes, which prove to be a hit with her.

Worried over whether Koizumi has a boyfriend, Yū follows her to a Western restaurant, where she seems to meet up with a bunch of guys. To her relief, Yū discovers that Koizumi was simply waiting for an open space in a ramen stand behind the restaurant. Later, Yū goes to a ramen restaurant with Misa, each ordering red Akamaru ramen and white Karaka ramen respectively, while Koizumi goes to it moments after they leave. During the weekend, Jun comes across Koizumi at a convenience store and tries out her recommendation of instant ramen.

Koizumi enjoys her latest favorite, Tomato Ramen, while Yū provides her own commentary. Upon hearing about the beneficial algae, euglena, Jun goes with Koizumi to try some green ramen which is rich in euglena. Later, Yū stands in a huge line for a popular ramen shop with the intent of switching out with Koizumi, getting angry with someone else when he cuts his friends in. In the end, they get told off by Koizumi and all decide to go to the back of the line to show their appreciation for the ramen.

Koizumi gets up early in the morning to eat some dried sardine ramen, catching the eye of Yū's older brother, Shū, who tries the same thing. On a hot sunny day, the girls take Koizumi's cue and try various types of cold hiyashi ramen. While attending a ramen fayre at a museum, Koizumi comes across a lost German girl named Hannah, sharing some of her ramen with her before helping her reunite with her mother. As thanks, she receives a voucher for some German-style ramen.

As summer vacation begins, Yū, Misa, and Jun go to an amusement park together before touring around Asakusa in yukata. Afterwards, Yū runs into Koizumi and decides to accompany her on a "nationwide" ramen tour around the city, trying ramen from across Japan.

While Yū and Misa go to the Katase Higashi beach, Jun accompanies Koizumi to a shop that serves local variants of instant ramen from all across the country, becoming curious about what career she is aiming for. Later, Shū and his friends go to an iekei-style restaurant to try ramen with rice, becoming awed when Koizumi enters the same restaurant.

Koizumi hikes up Mount Tsukuba in order to work up an appetite for its local ramen shop. Misa's younger brother Kenta tries to tackle the sizeable Buta Yarō ramen in Akihabara, he becomes motivated after seeing Koizumi easily manage the mega-sized portion. Later, Misa, believing Koizumi to have some secret behind her beauty, inadvertently ends up ordering a ramen full of back fat alongside her, leading to an addiction.

Yū becomes curious about a mysterious blue ramen that Koizumi was eating. Shū invites Yū to a conveyor belt sushi restaurant where they spot Koizumi enjoying one of its ramen dishes, prompting them to order some themselves. Later, Jun invites everyone to a Chūka restaurant in Kagurazaka to help her eat a massive gyōza her mother had reserved, with Koizumi ordering countless ramen dishes on top of it.

Yū tries to recall a tasty ramen she ate in Osaka when she was a kid, which turns out to be a dish literally called Tasty Ramen. After Yū and Koizumi go to a Tokyo branch at Kabukichō to try the dish, Koizumi goes on a ramen pilgrimage to Osaka where she encounters a woman named Ayane. Serving as Koizumi's bodyguard against guys trying to pick her up, Ayane accompanies Koizumi during her remaining ramen stops. Hearing about how Ayane is due to leave Osaka after quitting her job, Koizumi takes her to a ramen restraurant that she remembers from her childhood, but is later slightly disconcerted upon discovering that Ayane is actually Yū's cousin.

While heading home from Osaka, Yū ends up stranded in Nagoya after seemingly spotting Koizumi from afar and hopping off the train. With only 500 yen on hand, Yū goes to a fast food ramen shop, where she thankfully runs into Koizumi. Later in Autumn, Koizumi catches a cold and ends up taking several days off school, her continued absence taking its toll on Yū. After Koizumi eventually recovers, Yū decides to leave her alone to let her enjoy her first ramen in weeks.