Yakumo Hoshikawa is a supporting character in Himitsu no Aipri. He's Mitsuki Hoshikawa's older brother and fellow Aipri Club member. Yakumo is a quiet and intelligent boy, as he's always seen reading or talking about complicated subjects. He has a hard time expressing his emotions, which makes him come across as cold even to his sister, Mitsuki. Despite that, Yakumo is very popular amongst girls in his school.