Tsuki ha Higashi ni Hi ha Nishi ni: Operation Sanctuary

Naoki Kuzumi lost his parents in an accident five years ago and now lives with his aunt, uncle, and cousin Matsuri. He always figured his life was normal, except that he can't recall anything from his early years. One sunny day, while he's napping on a bench, a redheaded girl named Mikoto literally falls on him from the sky. For some reason, she believes he's her younger brother.