Briefly about The Hero Who Returned Remains the Strongest in the Modern World manga:
Morishita Taiju was transported into another world and became a hero, after wonderfully defeating the Demon Lord, he has returned to Japan. He was satisfied with his peaceful days as he hid his power, but… Hidden yokai and people with powers start to rampage, and the (rare nowadays) academy power battle-ish hidden world unfolds!! And Now He Trains Beautiful Warriors Using Superpowers!?
tl;dr: Isekai returner retains his OP skills after returning to Earth; discovers that Earth has more supernatural stuff going on than he expected. Gets dragged into various shenanigans, mostly via helping beautiful women around him.