We Are Preparing for the School Festival!
The Chaos Brigade has quieted down since their stunt in Kyoto so Issei and the others must now focus on other issues. After all, there are hero shows to act in, a school festival to prepare for, and the ever-looming Rating Game with Sairaorg...
Aired 29/05/2018EP 8 - We Are Preparing for the School Festival!

2018
High School DxD HERO
Issei and the 2nd years attend a class trip to Kyoto for well-deserved relaxation, leaving the senior and junior class students of the Gremory family behind. However, once there, they fall under attack and must win without Rias or their other powerhouses.
(Source: Anime News Network)
Note: Includes episode 0, Taiikukan-ura no Holy.