Right before his fight against Issei, Riser was able to gain the memories of his past life, Uzumaki Naruto. In the past Naruto lost his crush Sakura to Sasuke but also died trying to save a village that hate him.
Seeing his past self memories Riser refuses to become a loser like his past self, he will not lose Rias like he lost Sakura, instead he will make her his wife even by force and will create a harem and enjoy his life instead of dying trying to save the world.
