Migi&Dali

Synopsis (en anglais)

After finally adopting a child, the Sonoyamas were unprepared for the mystery that would soon unravel. Hitori seems to be the perfect son for his loving parents. He's handsome, intelligent, and grateful for his new lavish life—but he has a dark secret. Hitori is actually the twins Migi and Dali pretending to be one boy. And they have a terrifying motive behind their hidden identity. (Source: Crunchyroll)