Yamaguchi Kumiko, a new teacher at Shirokin High School, has been assigned to teach a class full of the school's most notorious delinquents. Unbeknownst to her fellow teachers, Yamaguchi is better equipped to deal with her rowdy students than most: as the granddaughter of the head of the Oedo family, she grew up around yakuza gang members and has learned to fend for herself. When one of Yamaguchi's students, Kumai, is accused of stealing a bag of money from the head teacher, she is forced to intervene to keep him from getting expelled. But is he really as innocent as he claims to be?

When the students create posters making fun of her and the head teacher, Yamaguchi learns that they have given her a nickname, "Yankumi", which she unexpectedly embraces. One of the students, Minami, is seeing a new girl. One day, he arrives badly beaten and gets into a fight with another student, Sawada. It turns out that the girl Minami is seeing was also going out with a boy from another school, who calls him out on the matter. Inspired by her grandfather's yakuza values, Yamaguchi encourages the boys to stick up for their friend.

A serial purse-snatcher is targeting women in the neighborhood near Shirokin High School, and Uchiyama, one of the students in Class 3-D, is a prime suspect. Determined to prove Uchiyama's innocence, Yankumi and a few of her students set out to catch the real thief.

Yamaguchi's fellow teacher Shizuka, who teaches English, is also working nights at a club in the Ginza district. One of Shizuka's students, Noda, who has developed a crush on her, gives her a necklace, and later follows her to the club, where he sees her throw away his gift. The enraged Noda posts pictures online, exposing Shizuka's second job to the principal, who threatens to fire her. After a talking-to from Yamaguchi, the principal promises not to fire Shizuka if all of the 3-D students can earn at least 30 points on their English midterms. Yamaguchi gets to work preparing after-school study sessions for the students, but will it be enough to save Shizuka's job?

Sawada finds Yankumi's lost phone and sets out to return it. In doing so, he ends up in a house filled with Yakuza and learns the truth about Yankumi's family from her grandfather. Meanwhile, the teachers are on the lookout for a violent gang of young men who have been attacking pedestrians, and Kumai has become smitten with a girl from another school, who he learns already has a boyfriend. Later that day, Kumai learns that the girl's boyfriend is the gang's next target. Concerned for her safety, Kumai rushes after them. While he is watching, the gang members corner the girl and her boyfriend, and the boyfriend runs off. What will Kumai do?

It's time for Shirokin High School's annual sports tournament, and the initially reluctant students of class 3-D have been goaded into participation by dismissive remarks from the head teacher, but they need one more student to field a basketball team. Incidentally, Yankumi has discovered that there's another student in the class, Yuki, who never shows up and she never even knew existed. But Yuki, who left because of bullying by Minami and Kumai, shows no interest in going back to school. Can he be convinced to return and face his fears?

Yankumi is struggling through parent-teacher conferences, but when it's time for Sawada's meeting, his parents don't show up. Later, he receives a visit from a girl who turns out to be his sister. Through these incidents, we learn that Sawada lives alone due to a falling-out with his parents. When his sister takes an unnecessary risk, Sawada steps in to save her, but ends up shouldering the blame and getting arrested. The next day, the head teacher announces his expulsion. Can Yankumi and the boys of class 3-D do anything to help?

Because of Shin's scary story, Yankumi is scared to walk alone to the school hallway. One time she left her phone and thinks that someone was following her only to find out that it was a little boy. The boy was Yuta Nakashima-sensei's step son. The boy think of the Nakashima as her mom but since they aren't blood related, Nakashima thinks they are not. How will Yankumi give Nakashima her senses?

Everyone is lovelorn that day. 3-D went to a group date wearing formal clothes to keep the fact that they are from Shirokin but soon was revealed. Yankumi saw her long time crush with a girl, and Tetsu the guy who has a crush on Yankumi forever felt that she'll never get Yankumi. But that wasn't the problem, one night, a boy fleeing from a video store he shoplifted from was bumped by the 3-D and were accused of steeling. How can Yankumi prevent them from being expelled?

As usual, Yankumi was called for her students got involved with cops but this time in a positive way. The 3-D became heroes and for some reason, Yankumi gave so much attention of herself although she didn't participate in the hero thingy. Meanwhile, a proud father was giving so much attention to his son which made him mad and say hurtful words . The father passed away all of a sudden. The boy felt bad and put himself in trouble. On the other hand, while Yankumi is trying to help him, some curious reporters found about her deepest darkest secret...

FInally the magazine stating Yankumi's back ground came out and made a lot of commotions. Yankumi was forced to resign but she doesn't want to. The students on the other hand were so mad about the bad article and were force to meet the press but instead of clearing things up, they made it worst for they beat the press. Now the Shirokin High has a reason to expel them and the only way for them to graduate is if Yankumi will resign. What will they do? Owe