Musuu (夢数)

Overview
Musuu (夢数, Dream Number) is a Yume Nikki Fangame produced by marisyan (まりしゃん), co-creator of dream book and sick mind. It stars Rei (零), a boy refusing to leave his room.

Gameplay
Like most fangames, Rei stays in his room, only being able to step out to his balcony, save at his desk, turn a space heater on or off, or sleep in his bed to enter the dream world. Uniquely, effects are referred to as Numbers, and allow Rei to match the appearance of the NPC he collects it from. Holding Shift allows Rei to run, meaning a speed effect is not needed.

Plot
Judging by Rei's attire, the meager heating in his room and the weather from his balcony, it can be inferred that he stays in his room due to a snowstorm or similar event.