Mesu Kyoushi: Injoku no Kyoushitsu

Following his parents' divorce, Takuya was raised by his mother after she remarried a man named Sanada. Life under the same roof proved unbearable due to Sanada's son, Eiji—a brilliant but arrogant stepbrother who constantly looked down on him. Unable to endure the hostility any longer, Takuya left home and enrolled in high school using his mother's maiden name, hoping to finally escape his troubled past and start anew. His fragile peace shatters when Eiji unexpectedly arrives at his school as a newly hired teacher. The situation escalates further when Takuya accidentally stumbles upon a clandestine meeting between his older stepbrother and Miyuki, a popular female instructor, inside an empty classroom. Realizing he now holds dangerous leverage, Takuya resolves to exact revenge against the brother who tormented him. To execute his plan, he enlists the cooperation of Rihoko, the school doctor, setting into motion a calculated scheme to seduce Miyuki and dismantle Eiji's standing from within the very halls where they both now reside.