Bokura no Mitsudomoe Sensou

Takahiko can't stand Aizawa, a student in another class. As for the reason why, it seems that Aizawa has his eye on Takehiro, a mutual friend. To save Takehiro from Aizawa's evil clutches, Takahiko plans an onsen trip so he can reveal Aizawa's true colors. However, when he hears about this idiotic plan, Takahiko's best friend Magi is nice enough to play along, but... Of course there's no way it could all go according to plan. The result is something Takahiko never anticipated! For the students at the same school, flowers of love bloom in total chaos!

(Source: Dangerous Pleasure)