Fukigen Itoko ga Kawaisugite Shikatanai

Haruki Togami adores his little cousin Naoki Koga. And Naoki, five years younger than Haruki, had been attached to Haruki since he was a baby. Over the years, Naoki grew from a cute crybaby into an angsty 18 year old high schooler, and Haruki doesn't know how to act around him. Even though his beloved cousin is thorny and grumpy all the time, Haruki sees Naoki's cute and soft side, but saying so just makes Naoki angrier. One night, after walking in on a suspicious bedroom scene between Haruki and his boss, Jin Fujioka, Naoki suddenly decides to move in with Haruki. Is Naoki really just looking out for his dear cousin? Meanwhile, Jin Fujioka, the infamous playboy and hardcore top, runs into a young Nachi Konno. Literally. To make up for it, and with the hopes that he might get lucky, Jin lets Nachi stay at his place for the night. Oh did he miscalculate big time.

(Source: Fantasista Inc.)