I seem to have regressed to a different timeline

At the end of the reception for his junior colleague's wedding, Kousei Shinzaki, in his thirties, unfortunately gets hit by a truck as he exits the venue. When he awakens, his body has reverted to that of a fifteen-year-old, yet he finds himself inexplicably in the modern world. In addition to this oddity, he discovers a family that should not exist and forms new relationships with them. For the second time, he embarks on high