Torikago no Tsugai

Torikago no Tsugai is a series written and illustrated by Minami Toutarou.

Plot
To search for a missing friend, 6 people arrived in a closed theme park, "Birdcage Castle" which should be deserted. However, in there, groups of two people are created and are connected by a chain, and now, the game of putting one's life on a line began!