Toku Kara Kikeomatsu: OST
"Two boys from opposing worlds, Isao Toru & Michi Yuuma, come across portals that appear to hold thousands of new worlds. After initial hesitancy, they decide to explore what these portals contain. But once inside, all light escapes, leaving them only with the audible remnants. Little do they know, each ‘world’ only a reflection of their own minds, and with every moment of evaluation, their sight returns, taking themselves on a journey of sanity and serenity.”
So what is this? This is the soundtrack to an anime that doesn't exist.