Yomi was the last villain on the show and a pretty good one.
He was once an ally of Kurama, back in the Yoko days.
And one day he was blinded by an assassin. Ironically, he grew so much stronger because of this.
And he found out later that it was Yoko Kurama that hired him because he became too reckless for the group.
Which created some friction in their new alliance.
Before he goes to war with Mukuro, Yusuke Urameshi proposes the Demon World Tournament.
And those two go up against each other near the end of the tournament.
Where he had to lower his power to enjoy his fight with Yusuke Urameshi.
And he wins in the end.
Mainly due to his son cheering him on.
He loses his next match due to his fight with Yusuke, so he goes on a new quest to get stronger and wiser.