That's Right, Let's Go to Kyoto
Issei prepares for his school trip to Kyoto, but before he leaves, he must go with Rias and the others to the Gremory household so Rias can report the completion of her family. There, they meet Sairaorg, who requests a little hand-to-hand with Issei.
Aired 17/04/2018EP 2 - That's Right, Let's Go to Kyoto
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.