Hiiragi-san Chi no Kyuuketsu Jijou

Every family has its own "secrets"... Shota Minamoto, a junior high school student, lives in an orphanage. One day, he is taken in by a family who lives in a gorgeous Japanese style mansion. Shota is welcomed with open arms, but the family has a secret that must not be revealed to the world.

(Source: Kodansha, translated)