: It is an anime-original episode based on characters from the light novel series by Ichiei Ishibumi .
The text you're referring to is likely related to , titled " The Unresurrected Phoenix " (also known as Yomigaerarenai Phoenix ). This is an OVA (Original Video Animation) released on December 9, 2015, following the third season. Summary of "The Unresurrected Phoenix"
: A 24-minute unaired OVA bundled with the limited edition of the 13th volume of the light novel. Highschool DxD BorN: Yomigaerarenai Pheonix Epi...
: Issei, having the same idea, catches Riser. They engage in a fight where Riser struggles to even glance at Rias's breasts, while Rias and Tannin watch from afar. By the end, Riser is considered to have successfully overcome his trauma. Key Production Facts Release Date : December 9, 2015.
For more detailed information or to watch the series, you can check platforms like Crunchyroll or visit the High School DxD Wiki for community discussion. [Spoilers] High School DxD BorN: Yomigaerarenai Pheonix : It is an anime-original episode based on
: Issei volunteers to help Riser overcome his fear in the Dragon mountains, with assistance from Tannin and Ravel.
: While the girls, including Rias Gremory and Akeno Himejima , are bathing at a nearby hot spring, Riser attempts to escape to sneak a peek at them. Summary of "The Unresurrected Phoenix" : A 24-minute
In this episode, asks the Occult Research Club to help her brother, Riser Phenex , who has developed a severe trauma regarding anything related to dragons after his defeat by Issei Hyoudou .