In Volume 14, when Riser heard news of his younger sister being kidnapped, he assembled his servants and to the human world to save her, however they arrives too late at the very end after the conflict had been resolved.
In Light Novel DX.1 short story "Phoenix of the Battle School Building DX?" (which takes place during Volume 19), Riser's Peerage has a rematch against Rias Peerage, only this time Issei was able to defeat Riser in the Rating Game.
Riser's younger sister who was a part of his peerage until his Rating Game with Rias Gremory. Following that Rating Game, Ravel was traded as her mother's Bishop piece until she could later be traded to Issei Hyoudou.
She later briefly returns to her brother's team to help him in his Rating Game against Diehauser Belial.