Yu Yu Hakusho

As the three strangers in Kuroko's house explain the reason for their presence, Yusuke begins to sense that something is amiss. These demons have come to him to reveal one thing: that Yusuke's ancestor resides as a king of Demon World! And unless Yusuke travels to Demon World soon, the balance of power could shift and spell the end of humans reign at the top of the food chain.