Koi wa Inamono Komarimono

One day, Takeda, an overly serious model student, suddenly received a passionate confession of love from his rival Fukamachi, a frivolous elite who's top tier in looks, brains and athletic abilities. Takeda has only ever seen Fukamachi in a hostile manner and he's been going all out in rejecting the latter's persistent advances. Then one night, he got dragged into helping Fukamachi who was out helping his private detective brother to look for a lost cat. That's when Takeda saw an unexpected side of Fukamachi who he always thought he would never be able to get along with... This is the bumpy high school romance between a carefree, frivolous and handsome natural genius and an overly serious and straightlaced model student who just don't get along.

(Source: Kaiohsha, translated)

Included one-shot: Sashinomi