Ryoko and her friends form Otogi Bank: a social club which specializes in resolving problems for classmates via aggressive transactions. The wallflower Ryoshi is smitten with Ryoko—despite rejection—and must prove his worth to the rest of the troop.

Ryōshi tells Ringo about why he fell for Ryōko, which Ringo tells her about later that night. The next day while the other members go shopping, Ryōshi hangs around the bank with Tarō Urashima, who quickly gets dragged away by Otohime Ryūgū when a female customer comes in, worried about having to see her violent ex-boyfriend. When Ryōko and Ryōshi investigate the meeting place, it turns out to be a trap laid out by thugs from Onigashima High School. Ryōko is overwhelmed and kidnapped while Ryōshi informs the other club members. Ryōko hides her true feelings of fear as she faces the gang's boss. Ryōshi and Ringo use his dogs to discover the base, and Ryōshi uses a wrist mounted slingshot to attack the thugs from the shadows, helping to set Ryōko free to join the fight. When the boss tries to take Ryōko hostage, Ryōshi fights him one-on-one and manages to beat him while fueled by his feelings for her before passing out.

Otohime is in a rivalry with Mimi Usami who used to call her names when she was a chubby elementary school student. They decide to enter a Miss Otogi Academy contest, and Otohime requests the assistance of the Otogi Bank to help her win. Both sides end up using slander campaigns on their opponents, while Ryōko and the other girls somehow get entered as well. In the end, neither of them end up ranking, but Otohime wins thanks to a solitary vote from Tarō.

When Ryōshi protects Otsū Tsurugaya from a stray baseball, Otsū, who is obsessed with repaying favors, becomes his maid and does all various things which makes him uncomfortable. While visiting Ryōshi's house to check on the situation, Ryōko and Ringo meet his aunt Yukime, an author who Ryōko is a big fan, who points out Ryōko's potential feelings for Ryōshi. Otsū soon gets a fever from overworking and collapses due to fatigue. The others learn about Otsū's childhood, where she was protected from a car by a boy who died before she could thank him, resulting in her having a fear of being unable to return favors. Ringo comes up with the idea of having everyone dress up as maids and serve Otsū, reminding her that there is no such thing as favors between friends.

Ryōko has trouble dealing with Momoko Kibitsu, a disciplinary committee member who is also a bisexual with a crush on her. Momoko comes to the Otogi Bank to request assistance for an attack on Onigashima High School. After getting through the initial waves of delinquents, the members are soon separated and communications are blocked off. Ryōko soon comes against Onigashima's student council president, Shirō Hitsujikai, who Ryōko fears greatly until Ryōshi and the others arrive to back her up, asking him to keep the delinquents in check. As the group wonders just what Shirō may be up to, Ryōko thanks Ryōshi for helping her.

Concerned about Ryōko, Ryōshi meets up with Ringo to ask about her relationship with Shirō, though she says it would be best to ask her himself once he gains her trust. Ringo recalls when she first met Ryōko in middle school and saw her true side for the first time. Noticing Ryōko pushing herself and getting into needless fights to hide her true feelings, Ringo came to understand her and offered her friendship. Ryōshi recalls when he started observing Ryōko and inevitably falling in love with her and decides to become stronger so he can protect her.

A girl named Ami Jizō has been secretly preparing food for baseball player Jin Hanasaki, as she has a crush on him, but is too shy to talk to him. Although he doesn't have feelings for her, he offers a date to repay her, with Ringo making it a double date with Ryōko and Ryōshi to ease her nerves. They go to the cinema, the arcade, the pet store and the park. Halfway through the date, Ryōko spots a cat stuck up in a tree and, upon going to rescue it, falls into the pond and hits her head. She ends up contracting amnesia, believing she's 13 years old, and has a completely different personality to her usual self. While Ryōshi looks after her in this state, Ami and Jin are left alone on their date. When Ryōshi and Ringo try to figure out how best to deal with it, Ryōko feels she is being ignored and runs off into the rain where she runs into Shirō. As Ryōshi catches up with her, he learns that Shirō assaulted her when she was younger and no one believed her, and he swears to hunt him down.

The Otogi bank receives a request to find Chūtarō Nezumi, the heir to a large company, a bride before his twelfth birthday. Alice Kiriki, Ami and Otohime are listed as candidates, but are rejected by his butler, Hammel, for their personality flaws. After several other failed candidates (including characters from Toradora! and Toaru Kagaku no Railgun), Hammel, after inadvertently insulting Ryōko, Ringo and Momoko, points Chūtarō in the direction of his childhood friend, Uika. The two get together, but Ryōko and the other girls are not happy about the pointless request and have the club president Liszt Kirki buy them all expensive cakes in apology.

Ringo is having trouble confronting her friend Himeno Shirayuki, who looks after seven siblings. When Ryōshi inquires the matter, Ringo explains that three years earlier, when she first became friends with Himeno, she discovered that she was actually her half-sister, and that Ringo's mother had taken over her house. Since then, Ringo had become unable to bring herself to talk to her. The next day, the Otogi Bank, along with Himeno and her siblings, go to a swimming pool, with Ringo continuing to hide from Himeno. When Himeno almost drowns trying to rescue one of her siblings, Ringo saves her using CPR, and the two finally have their long awaited reunion. The next day, Ringo convinces the school director, Ranpu Aragami, to give Himeno a special scholarship.

The Otogi Bank learned that someone has leaked information about their secret underground base to the press, believing it may be the work of Shirō. They decide to hold a discount on requests which makes everyone very busy. Ryōko, who had a strange dream involving Ryōshi, starts avoiding him. Later, Ryōshi encounters a cat-like boy named Saburō Nekomiya, who offers to train Ryōshi to be a real man. Meanwhile, Ryōko and Ringo find a beaten up Onigashima student named Reiko Kokonoo injured outside their dorms. She explains that she was a girlfriend of Shirō who was cast aside and left at the hands of the delinquents. Ryōko allows Reiko to stay with her while arranging for her transfer to Otogi. While Ryōshi trains with Saburō, Ringo asks Lizst to look into Reiko's background while Otsū keeps watch of her. However, Reiko turns out to be working for Shirō and Ryōko, along with several members of the Otogi bank are kidnapped.

As Ryōshi continues his training with Saburō, he learns of Ryōko's kidnapping. Ryōko wakes up in Onigashima High School where she is faced by Shirō. Tarō and Otohime get out of their kidnap situation while Majolica le Fay helps save Otsū and Alice and Mimi are saved by Litsz. Ryōshi and Saburō break through Onigashima's defenses with the help of Momoko and her subordinates and the rescued Otogi members. Sabōru explains that he once abanadoned Ryōko when she was in danger and felt guilty, hence why he decided to train Ryōshi. Ryōshi soon faces Shirō and, while initially overwhelmed by his fighting ability, remembers his training and feelings and lands a hit before Litsz declares the fight over. After Ryōko gives her thanks to everyone, they all go back to their lives.

A poor papergirl named Machiko Himura notices the supposedly expensive house Ryōshi lives in. Believing she can marry out of poverty, Machiko pops the question straight at Ryōshi, later requesting a date with him at the Otogi bank. Ringo drag Ryōko along to follow them on their date, hoping to get her to be more honest about herself. Machiko abruptly ends her date before she runs into some loan sharks, but Ryōshi saves her. Machiko reveals her motives, that her father ran off with her part-time job money and she is in debt. Ryōshi decides to call the Otogi bank before taking on the loan sharks, with Ryōko joining the fight. After the debt collectors are arrested, the Otogi bank pay off her debt and arranging her to stay at the Otohashi residence. Ryōshi later explains to Machiko that he can be manly because of Ryōko, who hears the conversation and is asked by Machiko to confirm her feelings for him.