Raizen is a youkai or a demon. He is the type of youkai who eats humans. He is one of the demons who raid villages for food and money and eventually kill the villagers. One time, he was badly hurt during a raid. A human lady doctor helped and took care of him. Soon enough they both fell in love with one another. It was said that the lady doctor was different from all the rest and the only woman Raizen loved enough to bear his offspring. When Raizen was well, he left. After that Raizen solemnly promised never to eat humans again.

           He interfered in the final battle between Yusuke Urameshi and Sensui Shinobu in Makai. Yusuke, who did not know anything about Raizen at that time won the battle with Raizen's help. However, Yusuke was not happy with his victory and was very determined to find out all about the youkai who interfered in his match and give him a piece of his mind.

        For a whole year or less, Yusuke trained very hard to be more powerful and to defeat his ancestor. The last time Yusuke fought with Raizen, it was then that Raizen's past was unfolded. Raizen told Yusuke about himself and how he met the lady doctor, who of course is Yusuke's ancestor too. Raizen passed away leaving Yusuke take over his place.