Ramune is a Doctor who specializes in treating patients with "mysterious diseases", which are caused when something "strange" sneaks into the hearts of the weak-minded. He is a foul-mouthed physician who is rude to most and very rarely understands the atmosphere around him. However, he is a very skilled doctor who can quickly identify the root cause of any strange illness. But because he always puts his patients first, he tries not to treat them too harshly.

Kuro is Ramune’s junior-high aged younger brother as well as his assistant. Not only is he a rationtional thinker with the ability to make split-second decisions, he has athletic skill to boot. While his usual calm demeanor and poker face make it hard to tell what he’s thinking, he never misses a chance to get in a dig at his older brother. Kuro has complete faith in Ramune when it comes to mysterious diseases.

The former owner of Akatsuki, she is capable of creating all sorts of mysterious items and remedies. Don’t be fooled by the fact that she’s a nine-year-old. Ayame has retained all her memories from her previous life of 103 years. Although she looks after those closest to her, she’s not above picking a fight or two. In fact, Ayame is more than willing to take risks so long as the odds of victory are in her favor.

Niko is both Ayame’s great-grandson from her former life and the current owner of Akatsuki. His warm smile and outgoing personality have made him popular among the local kids, who have fittingly dubbed him “Smiley Man.” He and Ramune have known each other since they were very young and have a sibling-like bond. A certain condition allows him to “see” more than anyone else.

A handsome face with an incredible amount of knowledge on mysterious diseases, Momiji is Ramune’s master. Tormenting those around him is one of his favorite pastimes, especially when it comes to a certain pupil. As he has a terrible sense of direction, Momiji always travels with Pipopo, a mysterious pet of his own design, to lead the way.