Love Equation(2006)

Koi no Hodasare Houteishiki

Sakata has just gotten a job teaching physics at a school staffed with more handsome faces than a host club. On his way to his first day of work, he mistakes the hunky vice-principal for a groper, and punches him in the face! However, because of a school policy pairing up each arts teacher with a science teacher, Sakata ends up sharing an office with that very same vice-principal, Ryuoh! One day, the straitlaced and ever-fault finding Ryuoh suddenly kisses Sakata...

(Source: Digital Manga Guild)