High School DxD, Vol. 9 (light novel)

It's finally time for the school trip to Kyoto. Pillow fights, midnight confessions...and it would be bad manners not to peek into the girls' bath, right? Issei is on cloud nine just thinking about it, but as soon as his class arrives, a brigade of monsters launches an attack, quickly turning an exciting excursion into a battlefield! It seems like a misunderstanding, but could there be more to all this than meets the eye?