Isekai Summoner, Shinwa no Kaibutsu-tachi to Gendai de Musou Suru: Uragirareta Moto Eiyuu wa, Aiomome na Nakama to Heiwa ni Kurashitai

Reima was a Summoner whisked away to another world, where he struck down the Demon King and was hailed as a hero. But the immense power that felled the Demon King soon inspired fear rather than gratitude—branded a threat to humanity, he was put to death. With a silent farewell in his heart to the summoned beasts who had fought at his side, he believed his life was over... only to awaken in a hospital bed in a parallel Japan. The world seems just like the one he came from, except that dungeons now await exploration and monsters roam free. Strangest of all, his summoned beasts are still with him! He's relieved to see them again, but it appears their devotion has grown heavier than ever before...