The demon Sword and the pure Ios are fighting their 101st battle during one of the many wars between pures and demons, when, both severely wounded, they fall on Earth, where each of them has to take the body of a human to survive; to their astonishment, the bodies they take are those of two twins, and, to make things worse, the angel has taken the body of the violent rebel Kanna, while the demon has taken that of the weak and defenseless Soma.
They can't use their powers, so they have to cope with being human brothers. But being without powers doesn't mean they don't have to fight, because creatures from Hell start appearing in this world, and most of them seem to be looking for the fallen demon Sword....
- Demon Sword
- Sword is possessing a weak human known as Souma. His main goal is to try to regain a new demonic body any way possible. As a human his demonic powers are limited to almost nothing. Later on he obtains helpful items such as bat cat, the devil spawn and fragments of Satan's soul. He also is currently attempting to overthrow Satan because Satan and most of Hell want Sword dead. For a low-level devil, Sword is stronger than most demons in Hell. Although in his human form, he always ended up in the hospital.
- A weak human whom Devil Sword has possessed. At first he is completely taken over by Devil, until for a short period Devil is put to sleep. Souma willingly allowed Sword to regain control, but with a mishap the reversal went wrong and formed a chibi version instead of possessing him. Souma, with Sword dormant inside him, must travel to Hell and become stronger. In Hell Souma learns a technique allowing him to shape his soul into anything he needs. Souma, learning this from Jill Herb, becomes the new successor this technique.
- Pure (tenshi) Ios
- Ios fell to Earth along with Sword during their battle, and ended up possessing the more thug-like sibling Kanna. Ios was a highly respected pure, but was banished because during an attempt to regain his body; for that to happen, he would have had to kill the soul of Kanna. He refuses and flees in order to save Sword and company. Ios used to be very powerful, but in times of peace (well, sort of) he was grown soft, for all Sword does is training and fighting.
- Kanna is the stronger of the two brothers. He acts as though he is a tough guy, but in truth he cares about his brother, friends, and Sword and Ios. Same as Souma and Sword, he is able to change when need be. When Kanna comes out he is much stronger, and Ios's wings turn black signifying, that he is an angel with a dark heart, similar to a fallen angel. Kanna is very powerful.
- Yakumi Soujirou
- Souma's best friend before Devil Sword entered his body. Both of them are in the Rokubou High Occult Research Society. Very interested in Occult things such as Black Magic,Summoning Ritual and much more.
- Souma and Kanna's childhood friend.When Souma didn't have Sword in his body, Nanami has always protected him from being bullied.
- A demon who used to disguise itself in the form of a cat. Her original form is a little girl. She helped Sword when he could not use his powers by clinging onto his back and provided him flight, and other various things.
- Mizuno Soujirou
- The younger sister of Yakumi Soujirou and a powerful exorsist.Her past is the reason why she wants to be an exorcist. At first,she thought Sword as a threat but after seeing him fight,her thoughts about him changed.