Umi no Mukou kara Kita Otoko

A port town in Tohoku, facing a sea dotted with beautiful islands. Minami grew up there and works for his grandpa, who runs a fishing business. Ever since Minami's father abruptly vanished, grandpa has been like a father to him. On Minami's 20th birthday, a mysterious man appears from the sea...!? That man's true identity is... A story of bloodstained destiny begins!

(Source: GOT Corporation, translated)