This feels like someone read the first volume of Arifureta and tried to copy it beat for beat while missing literally everything about the tone. Like, seriously...
Weak guy with a shitty skill goes into a dungeon, gets betrayed by a teammate and falls down a big hole, which he survives because there just happens to be magical super healing water at the bottom. When he wakes up he runs into a small/weak looking monster that actually turns out to be S ranked and which damages him before an extremely strong bear comes along and maims him in a way that he can't fully recover from. He drags himself back to the healing water, gets a better artificial replacement for the part that he lost, and then starts training by killing the 'weaker' monsters and stealing their skills thanks to a newfound ability. Once they feel like small-fries, he goes back for a climactic(? I feel like this one word is maybe the biggest difference between the plotlines and that's just sad) battle with the monster that maimed him, defeats it, and starts to escape the dungeon so that he can return to the real world as a stupidly OP monster alongside the supernatural waifu that he found in the depths of the dungeon.
Say what you will about Arifureta (especially after the first one) but whoever wrote it should be suing for copyright infringement.