High School DxD, Vol. 6 (light novel): Holy Behind the Gymnasium (High School DxD (light novel), 6)

ASIAS GETTING MARRIED?! Long ago, Asia used her Sacred Gear to save the life of a demon, a benevolent act that resulted in her being ousted from the Church. Now that demon, Diodora Astaroth, is back and hoping to wed Asia. She refuses, but the seemingly friendly man is persistent. As the Gremory Familias next Rating Game opponent, he wagers that if he wins, Asia will be his bride. Naturally, Isseis not about to let some pretty boy snatch up the blond beauty in his life, but Diodoras machinations may prove more sinister and cunning than initially suspected. Returning home with Asia could require drastic measures...