Bokura ga Koko ni Iru Fushigi.

Shinichi Manabe attends Seiryo High School. His father is a writer. 5 years ago, Shinichi went to see a mysterious mirage with Mio Fukamachi and Tamako Fujiomi. Mio is one year older than Shinichi and acts like his mother, while Tamako loves old samurai movies and likes to hug.

The mirage really was mysterious, and they had a lot of fun. However, a week later Mio tries to save a cat but ends up being killed. Shinichi hasn't seen a mirage since that fateful day.

One day, Tamako and Shinichi suddenly encounter another mirage. Shinichi pulls Tamako into the dense fog. Shinichi soon realizes that he is with Mio, not Tamako. He also realizes that instead of Mio, Tamako is dead. He asks himself, "Am I in a different world?" Looking for further clues, he flips through his album and finds many pictures he doesn't even recognize. He's now convinced that this isn't his world

[From Gamelex]