Saikyou Yuusha wa Oharai Hako: Maou ni Nattara Zutto Ore no Musou Return

Description from novelupdates.com :
There was a men who recieved a enormous gift and he became a hero. He was the one who made the biggest contributions for taking down the Demon King and he bring the peace to the mankin world, but… He was intercepted by the prince, who claimed all the honours for himself. He kicked out from the kingdom the hero just giving him a few golden coins. All his companions rejected him and showed him his hostily but the hero just acepted peacefully it and left.
The hero just retired to his home and started a slow life. But some persons starts to make hostile movement over him, and none of them was demons.
A men who became a true demon king and clean all the enemies. Raw : https://lhscan.net/manga-saikyou-yuusha-wa-oharai-hako-maou-ni-nattara-zutto-ore-no-musou-return-raw.html
Raw LN : https://ncode.syosetu.com/n0955el/