Above the Earth, there is a continuous battle between angels and devils. One devil in particular, Sword, has it in for a certain angel, Ios. In their 101st fight together, both are severely wounded. Not only that, but their clashing power causes the two to fall to earth. By chance, Sword finds a beaten, unconscious teenage boy nearby, and he is able to take over the human's body to save his own life. 8675w
Some time later, Sword awakens in the hospital, briefly confused about his whereabouts. The father of the body he possessed enters the room, extremely happy to see his boy Souma alive. Then the older twin brother shows up. Immediately, Sword recognizes his enemy's energy. Also nearly dead, Ios had ed with Kanna's body. Sword goes to attack Ios, but quickly realizes that the body is far weaker than his demon form, especially from being recently beaten to hell.
Since the brothers had been found heavily thrashed, their memory loss isn't that surprising. Their large change in behaviors is also explained by amnesia. As it turns out, Sword entered the body of the cliché nerd who can't run fifty meters without falling. Ios's new body is a terror, feared by all and constantly suspended from school. While the angel and devil have primary control over the bodies of the twins, reflex actions and memories of the other souls (still alive within the bodies) do appear. More importantly, the human bodies cannot handle the powers that Sword and Ios had used with ease. This a problem especially for Sword who is both over eager to use his powers and targeted by devils and angels.
Taken from doushi-sumeragi.net
15 Volumes (Complete)

To start, this was the first shounen manga I ever rode and ad first I didn't like the art but after the first few chapters I totally changed my mind! The characters were good and i felt a little with them, once I even cried a little^^ and I really enjoyed reading it ...houever the end was to rushed and to fast but even so it is devinitly worth reading!
This is the first manga Ive ever read and bought and I really liked it though the final battle and the end was really rushed if you ask me but I still read it and enjoy it very much
Like a lot of other people, I first read this title back in the day when it was originally being scanlated. Back then, there weren't nearly as many scanlation groups as there are now, so I was just really grateful to be reading a completed shonen series, no matter what the content. I reread it recently, and I must say, it just doesn't hold up. Parts of it bored me, parts of it annoyed me, and I had to skip around to make it to the end. (Which I shouldn't have bothered to do because I disliked the ending even the first time I read it.)
Rereading it, I was disappointed by a number of things. I didn't particularly care for the majority of the characters. I liked Sword, but poor Ios was so woefully underused for a co-main character. He was supposed to be as strong as Sword, but Sword got all the major fights (with Ios conveiniently absent). Even more bothersome for me, his character didn't really get any development. (How could he when he didn't get his own storylines?) He was the same from book 1 all the way to book 15, so it was hard to care about him when he was flat all the way through. Additionally, I positively loathed the main female. She spoiled large parts of the manga for me with her antics. She was uncute, inept, and had to be rescued far, far too often. (Plus, I found it two-faced of her to prefer Sword to the boy whose body he had taken over when the two of them had a longstanding relationship before Sword ever entered the picture.) There's truly nothing kind I can say about her. Additionally, the plot developments often seemed random and came out of nowhere, especially the final arc where (oh by the way) our main characters got sudden and inexplicable powerups. The ending itself is disappointing to boot--it IS an ending, at least--you aren't left hanging--but the ending that the mangaka chose is just unsatisfying. Except for nostalgia's sake, there's so much better shonen out there than this highly mediocre effort.
well it isn't the best but i read it for some reason since it seem kinda kool the story not that bad so worth the read