A 10 volume manga, also known as Bad Teacher Equation, created by Creator/KazumaKodaka. It also spawned two OVA.

Atsushi Arisawa enrolls at Jougaouka High School to be near Masami Shibata (Ma-chan), who was his childhood crush. Unbeknownst to Atsushi, however, Masami no longer works at the school and his older brother, Masayoshi is now the nurse. Atsushi mistakes Masayoshi for Masami and is horrified because to him, it appears that Masami's personality has done a complete 180. Add to the fact that Atsushi's friend, Kouji Inagaki is totally in love and constantly trying to make-out with him.

Due to all of this mess, Atsushi's life at Jougaoka is hell... until he starts thinking that maybe the new Ma-chan isn't so bad afterall and that, maybe he actually likes the way Ma-chan is now. Until of course, he finds out that Masayoshi isn't Masami... but after a while, he still ends up falling in love with him for what he is.

!!This manga provides examples of:

* EightiesHair: Most notably Masayoshi who sports a mullet. Thankfully, ArtEvolution kicks in and is not as noticeable in later volumes.
* ArrangedMarriage: [[spoiler: Masayoshi and Mizuha go into an arranged date. They decide to stay friends as Mizuha notices he's falling for someone else... Atsushi.]]
* ArtEvolution
* AttemptedRape: [[spoiler:Masayoshi, when he was a high school student, was almost raped by the same guy from the OVA that was gonna sexually assault Atsushi.]]
** It turns out that [[spoiler: Masami also had an incident like that in the past. He thinks he's "DefiledForever" and doesn't want to have sex with his boyfriend Tooru due to this.]]
** And almost at the end of the manga, [[spoiler: Yuriko almost falls victim to DateRape during a school tour and Kouji rescues her. It foesgoes into RescueRomance as that gives them the push to admit their feelings.]]
* BetaCouple: Tooru and Masami. [[spoiler: Yuriko and Kouji]]
* BiTheWay: Kouji is in love with Atsushi, but he also has a bit of SlapSlapKiss with local yaoi fangirl Yuriko. [[spoiler: When Atsushi chooses Masayoshi, Kouji and Yuriko end up together.]]
* {{Bifauxnen}}: [[spoiler:Mizuha Toda]]
* ButNotTooForeign: Masayoshi and Masami's deceased mother was from Norway, while their father is Japanese.
* BoysLove
* CantHoldHisLiquor: Masami and Masayoshi. Kouji to a lesser extent.
* ComingOutStory
* CuteLittleFangs: Kouji
* FirstKiss: [[spoiler: Masayoshi kisses Mizuha in chapter 25.]]
** Kouji and Atsushi shared their first kiss when they were children, promising to get married when they get older.
* GeniusDitz: Atsushi
* GenreShift: It starts as wacky comedy with some touches of yaoi romance, but later becomes much more character-driven and borderline melodramatic (if not downright ''{{wangst}}y'')
* [[{{Hot For Teacher}} Hot For School Nurse]]: Atsushi falls head over heels for Masayoshi
* TheIdiotFromOsaka: Kouji
* [[spoiler: IntimatePsychotherapy: Masami and Tooru ''finally'' reach third base after Masami spills out his traumas and Tooru tells him he's ''not'' DefiledForever by them.]]
* ManlyTears: Tooru sheds these quite often.
* SecondLove: Atsushi's first love, Maa-kun, was Masayoshi's younger brother Masami.
* [[{{Seme}} Seke]]: Masayoshi and Atsushi wind up switching roles, when Atsushi was in high school, he was the {{Uke}} and Masayoshi was the {{Seme}}, when Atsushi is an adult, he's the {{Seme}} and Masayoshi is the {{Uke}}.
* TallDarkAndSnarky: Masayoshi, despite not being darkhaired.
* {{Tsundere}}: Masayoshi and Yuriko are both type A
* YaoiFangirl: Yuriko