Bad Teacher's Equation (Kusatta Kyoushi no Houteishiki) is a Boy's Love Manga created by Kazuma Kodaka, which was serialized from 1993 to 2002 and compiled into 10 volumes. 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 after all 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:
- '80s Hair: Most notably Masayoshi who sports a mullet. Thankfully, Art Evolution kicks in and is not as noticeable in later volumes.
- Arranged Marriage: Masayoshi and Mizuha go into an arranged date. They decide to stay friends as Mizuha notices he's falling for someone else... Atsushi.
- Art Evolution
- Attempted Rape: 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 Masami also had an incident like that in the past. He thinks he's "Defiled Forever" and doesn't want to have sex with his boyfriend Tooru due to this.
- And almost at the end of the manga, Yuriko almost falls victim to Date Rape during a school tour and Kouji rescues her. It foregoes into Rescue Romance as that gives them the push to admit their feelings.
- Beta Couple: Tooru and Masami. Yuriko and Kouji
- Bifauxnen: Mizuha Toda
- But Not Too Foreign: Masayoshi and Masami's deceased mother was from Norway, while their father is Japanese.
- Boys' Love
- Can't Hold His Liquor: Masami and Masayoshi. Kouji to a lesser extent.
- Coming-Out Story
- Cute Little Fangs: Kouji
- First Kiss: 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.
- Genius Ditz: Atsushi
- Genre Shift: It starts as wacky comedy with some touches of yaoi romance, but later becomes much more character-driven and borderline melodramatic (if not downright
wangsty) - Hot For School Nurse: Atsushi falls head over heels for Masayoshi
- The Idiot from Osaka: Kouji
- Intimate Psychotherapy: Masami and Tooru finally reach third base after Masami spills out his traumas and Tooru tells him he's not Defiled Forever by them.
- Manly Tears: Tooru sheds these quite often.
- Second Love: Atsushi's first love, Maa-kun, was Masayoshi's younger brother Masami.
- 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.
- Tall, Dark, and Snarky: Masayoshi, despite not being dark-haired.
- Tsundere: Masayoshi and Yuriko are both type A
- Yaoi Fangirl: Yuriko
