Raizen was a pretty interesting character on the show.
For many thousands of years, he was inarguably the strongest demon in all of demon world. However, a personal choice he made eventually led to him having two very powerful rivals.
We first see him actually possess Yusuke Urameshi during his last fight with Shinobu Sensui. After taking over the Spirit Detective, he easily crushed Sensui.
We find out that he’s actually Yusuke’s distant ancestor.
And his part-demon offspring is quite furious about the whole body stealing thing.
Turns out he had fallen in love with a woman from ancient Japan. Unfortunately for him, his stomach only allowed human flesh to give him nutrients. He vowed not to eat humans until he saw her again, and I believe she died in childbirth before he ever came back. Leaving him to go on starving for many years afterward.
After advising Yusuke on what to do about the politics of demon world, he finally succumbs to an empty stomach.
During the final moments of the show, they finally make their peace. I will say it’s retarded when fans thought he was actually Yusuke’s father. He may have used the word, but it was obvious that he had never met his mom.