I am trying to find the manga where the main character gets a letter of introduction from the Spirit King, Demon King, and the Dragon King.
- He also uses his power to change his age so that he can get in the school.
- He had a supposedly legendary bird to get the letters.
- He went to school with the Demon King's daughter who at first he thought was a son.
- The introduction letters caused a huge commotion between the teachers and principal. -On the first day of school he summoned the spirit king, which broke a barrier.
- He was a guy who fought the demon king after the hero lost.
- Magic school.
- Everyone had human like features.
- He joined the school with a girl from an aristocrat family.
- He knew ancient magic but wanted to learn new magic.
- He was in a tower studying books for a few centuries.
- Seen by elves as a heroic figure of some sorts.
I don't remember if it was in color or black and white.