DXD: The Retired Hero

Reincarnation wasn't new to him.
He was once an excited teen, ready to save the world from the demon king, now he was a veteran, a man that had gone through countless wars and came out as a victor, a man that mastered countless forms of battle.
Somewhere along the way, saving the world became a chore, so he discarded the sword and took up magic for the next few dozen lifetimes.
Magic was there whenever he was sent to another world, his body, on the other hand, needed work, so he made sure to study the magic of every world he visited, Holy, dark, demonic, water, lightning, the list went on.
So... Now, this man had one question...
Why the hell was there a magical girl here?

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I own nothing, just the OC.
This will be a stress relief since moving out for college is stupidly complicated.