High School DxD, Vol. 9 (light novel)

A KIDNAPPING IN THE OLD CAPITAL!
Issei and the other second-year students at Kuou Academy are off to visit Kyoto for their school trip. Everyone’s excited for a few days of sightseeing and souvenir hunting.
However, the fun comes to an end when the Hero Faction of the Khaos Brigade abducts a local fox spirit princess! Issei’s not about to let some villains get away with taking an innocent woman (especially not one with an ample chest!), but his opponents are descendants of mythological champions. Worse, they’ve all got Balance Breakers! Does the Red Dragon Emperor stand a chance without his beloved Rias by his side?