With no money and no where to go, Natsuno has been crashing at his office after breaking up with his girlfriend. Natsuno reunites with Ui, a friend from high school who had a crush on Natsuno, at a mutual friend's wedding, but due to a recent accident, Ui has amnesia and can't remember him. When Ui reject Natsuno's request to stay with him for a while, Natsuno uses his amnesia to his advantage and tells Ui they used to be a couple. Ui will let him stay if he can prove it.
Poor college student Kusumi hits novelist Kijima with his bike, breaking Kijima's arm. Unable to compensate Kijima for his injuries, Kijima offers Kusumi an deal where Kusumi transcribes Kijima’s latest story as he orally dictates it. But, Kusumi is surprised to find out Kijima write erotic novels.
Afraid of the outcome if others found out, popular and lively Todo is hiding the fact his penis is very small and he has inverted nipple. However, while on a class trip, Yamato, Todo's polar opposite, gloomy classmate, discovers his secret. Yamato shares his own secret, he has no pubic hair, and gives him advice. The two start practicing together to improve Todo's body.
Hazuki is a socially awkward and earnest member of the product planning department, who hates seeing couples in public and his coworker Watanabe. Watanabe is a popular member of the same department that Hazuki thinks he is superficial. But, Hazuki's feelings change when Watanabe invites Hazuki to eat with him at his house on the weekend. Their new friendship develops into a relationship, but things go wrong when Hazuki discovers Watanabe was seeing him as a replacement for someone from his past.
Leaving for university, Rikuo opens his door to find a man claiming to be the stray cat he helped two weeks ago. The man says he wants to repay Rikuo and asks to stay with him. Rikuo initially rejects him, but, when he feels bad for the man after he returns to find him still in front of his door, Rikuo allows the man to live with him and begins calling him Tama. However, Tama isn't a cat, but the president of a company who fell in love with Rikuo after seeing him care for the real Tama.
Ch. 1-2: After his beloved childhood dog and only friend, Chibita, dies, Kei wakes up to find a man in his house claiming to be Chibita
Ch. 5: Aki wakes up in a love hotel next to his childhood friend Oosawa, who claims they had sex. When Aki can't remember or believe him, Oosawa suggests recreating the night
Ch. 5: In order to pick him up, playboy Kisa pretends to be Hana's former classmate. But, during their date Kisa actually falls for Hana.
To impress the girl he likes, Hoshirou studies hard to get into a prestigious high school, but mistakenly enrolls in a boys' school. The tanuki statue behind the school dorm has a legend that, if you write the name of the one you love on its scrotum your will be fulfilled. Unable to give up on love, Hoshirou sneaks out to write the name of his crush Nozomi. While writing, elite, popular student Nozomu catches Hoshirou and, thinking Hoshirou's writing his name, tells Hoshirou he'll be his lover.
In high school, Natsuka fell in love with his popular and elite classmate Hakushima but never confessed due to their differences in status. After 4 years, now in college, Natsuka, still in love with Hakushima, has been sleeping with his sex friend Seno, who is the exact opposite of Hakushima, to relieve the stress of his unrequited love. However, one day, after Seno and Hakushima get into an accident and end up unconscious in the hospital, Hakushima wakes up in Seno's body.
Ch. 6: When friends Kuratani and Shinonome try to enter a couples only cake buffet, they are turned away due to it being for straight couples only. Wanting cake no matter what, Shinonome decide to crossdress. Though the plan to enter works, when the boss asks for proof they're a couple, Shinonome kisses Kuratani and he can no longer hide his crush on Shinonome.
Warui Otona ni Narimashite