Youmi is another master of Makai who mainly organized the Ankoku Bujuustkai.

In his younger years he fought alongside Youko Kurama in his band of theives until he branched off and created his own group because he didn't want to listen to the clearly smarter Youko Kurama. After this happened, Kurama had an assassin sent to kill Youmi, but the assassin failed and merely blinding him (a mistake that cost him his life through years of torture).

Many years later in Makai, the high master demon Raizen (Yusuke's father) was dying because he'd refused to eat humans. During his last months, Raizen called Yusuke to his side to train him for the upcoming Ankoku Bujuustkai. Youmi had called upon Kurama to help him, (not knowing it was Kurama who sent the assasin), and Mukuro called upon Hiei.

Soon after Raizen died, the Ankoku Bujuustkai was on. Kurama soon abandoned Youmi to team up with Yusuke. After this happened, Youmi recruited his son Shura (who he'd been genetically creating in a lab) in Kurama's absence.

The Ankoku Bujuustkai finally began and the first major battle involving Youmi was him versus Shura. He defeated Shura (with some difficulty) and then went on to fight Yusuke. The final fight was very explosive, and ended with Youmi barely winning. He was then defeated in the next round by a common demon because he was just too weak. After the tournament, he congratulated Yusuke for the fight he put up, and challenged Yusuke to a rematch at the same tournament in three years. He then went off to train.

INFORMATION FROM ABSOLUTEANIME.COM