One: Kagayaku Kisetsu he (1999)

One's story revolves around Kouhei Orihara, the main protagonist, who suspects that at some point his current life will change while living a peaceful daily routine. Due to this, he begins to seclude himself in the Eternal World, a world within his mind. The game's main recurring motif is a focus on the Eternal World, a mystical alternate space which is never clearly explained, and the details of which are unknown.