Twilight Syndrome: Tansaku-hen (トワイライトシンドロム：探索編, lit. "Twilight Syndrome: Search volume") is a Japan-only video game developed and published by Human Entertainment, released on the Sony PlayStation in 1996. The game was written and directed by SUDA51.
Twilight Syndrome: Tansaku-hen is set up as a mystery, requiring the player to travel around the game's environments attempting to discover the truth behind the so-called "Twilight Syndrome." Progression is divided into chapters called "rumours," each of which has a good ending, a normal ending, and multiple bad endings; the good and normal endings result in the protagonists learning a little more of the truth, while the bad endings result in the character's death. Naturally, the player must achieve either the good or normal ending in order to advance to the next rumour.
The op song is called "Crystal Rain," by LOVEFIXER.