Falling Into Love(2006)

Kono Kimochi wa Koi ni Naru

High school student Hisashi has admired top model Tomohito for years. His only goal in modeling is to get a contract at the same agency. By sheer coincidence, the two happen to be at the same shooting location. Looking to put some fear into his rising competition, Tomohito snares Hisashi into a passionate kiss claiming “I just wanted to wipe that prim look off your face!” But even the best laid plans are bound to have complications. Instead of running off the competition, he may have just gotten himself a suitor! (Source: 801 Media)

Also includes the oneshots:
Prepare Yourself
Two romantically involved cousins work at a detective agency and are sent to solve a case involving a girl that won't leave her room.

I Want to Be With You
Young uncle Kyou and his middle schooler nephew Taichi are dating. Kyou also used to date the Taichi's father, his sister's husband, and Taichi is still jealous over that.

Love's Recommendation
Two highschool friends are attracted to each other but one of them refuses to admit his feelings.