Puzzles on an Isolated Island

Kotou Puzzle
孤島パズル

Prequel

Moonlight Game
Gekkou Game· 月光ゲーム
manga

The Eito University Mystery Novel Study Group (EMC for short) encounters a tragedy at a campsite during a summer camp. Lured by the magic of the moon, the four EMC members take on the murderous demons that appear! (Source: Mag Garden, translated)