Saikyou no Maou ni Kitaerareta Yuusha, Isekai Kikansha-tachi no Gakuen de Musou suru

Kyouya Kujou is a boy who was unable to save the world because he does not possess the unique abilities that are the blessings of a goddess. In another world where returned heroes who have saved many worlds gather, he is a boy who could not save the world. In the academy, he was ridiculed as a "Failure Hero." However, he is the most powerful and unique hero who trained for 30,000 years in another world with Felice, the most evil demon king who has destroyed 3,000 worlds! Kyouya's latent ability is so powerful that even the strongest heroes cannot compete with him...? The tale of a boy trained by the most powerful demon king is about to begin! (Source: Hobby Japan, translated)