Naoto Tachibana is the younger brother of Hinata Tachibana, a detective in the organized crime department of Tokyo, and the "trigger" for Takemichi Hanagaki's time travel powers. As an adult, Naoto is a righteous individual who is also determined to alter save his sister. He has a no-nonsense personality and is usually unamused by others' humorous advances. He is also willing to embrace far-fetched possibilities, such as the fact that Takemichi can time-travel, and even make his own hypotheses about it.