In this arena, Felpe was facing off against an ancient powerhouse. Felpe's solitary nature meant he had few friends, but his hot temper from practicing fire magic caused him to offend many, including the ancient warrior he was now confronting.
The original cause was still to help Delas; at that time, Felpe hadn't yet been injured. He was still that highly sought-after genius, an ancient warrior of renown, so the other party was forced to be tolerant. However, upon hearing that Felpe was injured and crippled afterward, the adversary had been longing to seek revenge, but no one except Delas knew Felpe's whereabouts. And clearly, Delas was not about to betray a friend to an old enemy—even though that friendship was only on the surface.
But now, Delas was dead. And since Felpe had appeared on his own, the opponent certainly wasn't going to miss this opportunity. It could be said that he joined the Ancient Powerhouses Alliance not to confront Long Yi but purely to take revenge on Felpe.