User blog comment:B214/Volume 23 discussion blog/@comment-172.58.16.90-20170407013301/@comment-10330822-20170407033809

Have you been reading the extra chapters too? Because that is where the character development is for Riser.

In one, it is shown Riser fell into depression after being beaten, and Issei comes to his house to take him to Tannin's territory. There, he helps Riser get over his fear of dragons and re-gain his "fortitude". During which, they fight and Issei beats him again, and wins Riser's respect. Riser agrees to give up on Rias, but wants to see her naked body just once, and that starts another fight.

In another, Riser and Rias agree to a re-match of their Rating Game, and Issei fights Riser again in a honorable fight and wins again. There isn't mentioned to be any lingering hostility between them, but Riser still seems to want Rias and wants to challenge Issei for her.