Kei and Minako live in a world where demons exist. But like most ordinary high schoolers, they had no idea. Life in the small city outside Tokyo went on much as it does in the real world.
One day Mamoru appears and tells Kei that she has his soul. He tells her of the demon world, the true existance of magic, and more. Furthermore, he gives TB to Kei as a pet for proof of his claims. TB, being a cute baby demon, sways Kei to accept his outrageous story thus far.
Mamoru goes on to explain that because Kei has his soul, and it is not in his own body, that he is immortal. And because of this, it makes Kei and Mamoru the only humans in the world who can kill the evil demon king. Mamoru's immortality makes him a great fighter, but it also involves a sad past.
With Mamoru, Kei and Minako suddenly find themselves fighting demons while they are supposed to be studying for college entrance exams. One demon they meets is Maejin Zasz, who is determined to become the next demon king. He tags along with the group, waiting for them to find, fight, and kill the current demon king. Maejin is shy and mellow and they all end up becoming friends.
Enter Hunter Weaver. He is a demon hunter, a mercenary usually employed by various governments to kill demons. His newest target is Maejin, so he gets dragged into the gang's mess with the demon king.
Hunter soon discovers that Maejin is an Ok guy, so he agrees not to kill him. That, and Mamoru's immortality means that Hunter would get his a** kicked if he tried to kill Maejin.
The group goes off to fight the demon king. They discover they've developed quite a bond, and they succeed. Mamoru overcomes his past and confesses his love for Kei. She feels the same and the two become a sickeningly cute couple. Maejin becomes the new demon king, and is a kind and intelligent ruler. Minako develops some magic and uses her gifts to start a career as an idol singer.
Kei and Minako get into collage and meet their old friend Merili. Merili happens to be a hanyou (half demon), and now that the girls know all about the demon world, the three of them develop a tighter friendship. Just when everything looks wonderful, Alexis shows up.
Alexis is Hunter's wife. She had been in a demonic spell-induced coma caused by the old evil demon king. Hunter is amazed and overjoyed to see his wife awake. But Alexis is pissed. She woke up in America, knowing only that her husband had left her behind and gone to Japan. Alexis also thinks (as Hunter once did) that Maejin was the one who put her in a coma. So Alexis tries to kill both Maejin and Hunter for a while. But Kei and Mamoru (who have always been nice to her despite her wanting to kill their friends) convince her it was all a mistake. Hunter had left Alexis to avenge her, which he did when he helped the group kill the old evil demon king.
The whole situation is explained and everyone is happy again. Hunter and Alexis take a long overdue honeymoon, but return to Japan to help the group as always. More stuff happens. Bad guys come and are defeated. Maejin finds his long lost sister, Toku. Mamoru and Kei eventually marry.
Now all that's left is Maejin and Minako. The two of them always had some tension. Minako has the ability to summon Maejin at will, just as Mamoru could force TB to appear for Kei. The situation leaves Maejin feeling both inadequate and attracted to Minako. Kei and Hunter try to play matchmaker, but in vain.
A different sort of evil demons appear, killing an old friend of Maejin's. Maejin feels responsible for her death and adopts her two now orphened twins. Maejin is many things, including a warrior, a politician, and a businessman. But he is clueless when it comes to the twin one year olds. Minako steps in to help raise the babies. When they start calling her 'mama' and Maejin 'papa', it's official. Minako and Maejin finally get married.
Fast forward to the gang and their now teen age children. There is some more drama, but soon the story winds down. SOUL ends happily with one big happy familiy. The End.
