Dear Gentle Papa(2001)

Haruhiko has just been confided by his friend, Kyotarou, that he is seeing someone. That "significant other," turns out to be Nao, a young elementary school boy. Nao's mother died when he was younger and the only person taking care of him is his dad, Hirofumi. Scared that Hirofumi might find out about their relationship, Kyotarou asks Haruhiko to tag along on their outings to disguise the relationship from Hirofumi. Haruhiko reluctantly agrees but what he hadn't expected was to develop feelings for Nao's father.