A Diffusion Disease

Katsuhiko Tobe faces an odd dilemma. Losing control of his physical self, his body diffuses into nothingness as his disembodied consciousness flows throughout the world constantly contemplating both the world and his current situation. Meanwhile, his best friend Azami Seshimo waits in their native Japan for Katsuhiko's return.

(Source: Anime News Network)

Note: the 1st edition also includes 2 short-stories.