Mysterious disease" is a disease caused by “mysterious” existence. Koto-chan, who suffers from mayonnaise coming out of her eyes, comes to Ramune, a doctor specializing in such diseases which can’t be explained by current medical science. She is brought there by Kuro, Ramune’s disciple. Ramune offers a mysterious tool to heal Koto, who also confesses more seasoning comes out of her eyes in addition to mayonnaise.