Myriad Realms: Bai Wunan's Transmigration Journey

“It's time to go back.” The quiet words fell. Now this peerless powerhouse would return to the earth and correct the mistakes he had left behind. There was no longer any chance of allowing the evil personality to survive on this land. Now is the time for me to send you down.

(The protagonist returns to Earth during Bai Chou and Sha Ya's decisive battle, but his power will grow very slowly. He probably won't return until the second volume, after going through Warhammer 40K, FGO, Hu Hai II, and a whole lot of other worlds, so the early part will be long and span all kinds of worlds. Of course, if there's anything you'd like to see, the author might write it in after doing some research, so feel free to comment. Haha.)