All I can remember is in the first few chapters the reincarnated person with his class walks down a dungeon and eventually a lot, a shut ton of monsters come and because the hero in the class see's this he tells everyone to retreat while some are being eaten alive. When everyone starts running the MC is the last one up and is pushed down the stairs and is eaten... Only weird thing is that even though MC was eaten he wakes up like as if he has multiple lives and sees the monsters eating his flesh.

I forgot what happens but after waking up and some stuff he eventually goes inside some room and finds this chick who is his classmate and saces her, she eventually out of fear and reassurance follows along MC, the hero actually used her as bait and she reveals that to MC some point.

Thats all I can really remember. Thanks.

it's awfully sounds like arifureta but what you said is so different since this one is adapted to manga and the girl he found in the dungeon is not his classmate

Im pretty sure its before arufretta, The main thing being the power which is how when MC dies he comes back but stronger.

And I just found it too, Suterareta Yuusha no Eiyuutan, or, he Forsaken Hero Returns From Death to be the Demon King