Oshiete FGO!: Ijin to Shinwa no Grand Order

To save the world from destruction, a Master, Gudao, summons Heroic Spirits and fights alongside them. He tried to learn more about the Heroic Spirits to understand them better and deepen his bond with them, but it was too difficult to learn and he understood nothing... That's why, let's get the heroes themselves to teach him about their history and legend!

(Source: Kodansha, translated)