The eldest son of his family, Haru Kaidou, received news that his mother was dying and quickly traveled to Canada. However, upon reaching there, he discovered that his mother had lied to him - he was now responsible for his adopted brother, Ren Kaidou, who was a secluded child that preferred the companionship of dogs over humans. Haru struggled to connect with Ren due to his untrusting nature, but eventually, he managed to establish a bond with him. Haru made a promise to live with Ren in Japan after he graduated high school, but an accident made him lose all of his memories of their relationship, including the pledge. Five years passed, and Ren arrived in Tokyo, expecting Haru to fulfill his promise - but Haru had no memory or knowledge of their brotherhood. To Haru, Ren was just a stranger asserting to be his sibling.