Yubelluna "The Bomb Queen"

Riser's Queen and the strongest member of his peerage, also known as the "Bomb Queen" (爆弾王妃（ボム・クイーン） Bomu Kuīn) due to her powerful fire magic that looks like a bomb explosion when hitting the target.

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She defeated Koneko, Akeno (albeit with the use of the Phoenix Tears), and Yuto at the Rating Game between Rias and Riser. She is Riser's favorite piece, as he often makes out with her and fondles her.

(Source: Wikipedia)