Kamen Rider: I Am Ark

After a university opening ceremony, the Den-O train rushed past Chiyo Ikki and swept him into a space-time tunnel. Thus began his fifteen years of wandering through the world of Kamen Riders.

He personally fused with the Ark, stabbed the Lord of Truth in the back to seize the Book of Omniscience and successfully decipher it, then betrayed the newly born Zhuge Liang at the height of his confidence and plundered all his alchemical knowledge. He sliced Giff into tiny pieces for research, and when DGP couldn't take it anymore, they “kindly” brainwashed Sparrow and forced him to his death... After countless journeys between worlds, he finally returned to his hometown.

Coming home should have been a happy occasion, like a wanderer returning to his family.

But...

Wait, what did you say? What do you mean the huge rift created when I transmigrated gave rise to monsters in my original world, leading to the appearance of magical girls?