Itazura Neko no Memento

With his renowned-novelist dad away from home and his mom busy with her own job, Wataru's parents hires a young male housekeeper named Osaka to help around the house. From the moment they meet, Wataru considers Osaka's relentless efforts to be part of his life a nuisance. That is, until he receives a letter that helps him start opening up. The anonymous letters Osaka continues to bring him are sweet and caring-but Wataru believes they're from Osaka himself. Wataru decides to confront Osaka directly.