He's killing his own kind, adventurers like he used to be. leaving behind their friends, f...

I'm not suggesting you have to like the story but it's clearly stated that he's NOT killing because he was fired. It's a similar plot to a different manga on here, where he was basically turned into something other than human once he agreed to the contract. He has a moment of self doubt where he asks if he's a monster for not feeling anything after the first kill and he's told that it's a result of the contract. And he later has a conversation with one of his former team mates where he states he's not mad and actually thankful that he was fired. Before, he hadn't felt like he belonged and now he finally feels like he's found his purpose. And also, now that he's part of the dungeon, if he doesn't defend it, he'll die. It's a form a self defense.

If you want a more wholesome story that doesn't involve senseless violence, there's a lot of them that are fun.

Maou ni Natta node, Dungeon Tsukutte Jingai Musume to Honobono suru. The better done version of this story. A young man becomes a dungeon master in his second life. Not too much focus on fighting, more about building a found family and then clearing up any issues that might bother that family.

Leveling up by only eating. A young man enters an online game world in order to change himself. He focuses on playing the game only by eating tasty food. Funny and fun, it's nice to see the progress of the story. Most of the solutions are food based and don't require much fighting.

Spirit Farmer. A young man gives up on his dreams to be a famous adventurer and returns home to be a farmer, only to discover he has an amazing skill. The only catch? It's related exclusively to farming and can't be used outside of it. Very cute, family oriented.

Hitoribocchi no Isekai Kouryaku. An entire class ends up in another world. The MC tries to escape but fails. As a result, he ends up with terrible skills and must find creative ways to use them. Mostly focuses on teamwork, with the MC sometimes sneaking off to try to solve things on his own.

Trash of the Count's Family. A young man ends up in the body of a villain. He decides this is a great thing and if only he could avoid one or two upcoming problems, he'll be able to live a lazy life. The only problem is that he ends up solving things too well, which gets him more and more involved with the heroes. What's going to happen to his lazy life? Very funny, there's some fighting but it's not the main focus.

Clever Cleaning Life Of The Returned Genius Hunter. A man is sent back in time after not appreciating how good he had it as an adventurer and he's forced to start from the ground up, doing a job he used to think was pointless. Unless he completes mysterious missions, he can't unlock his old skills or get his life back. Focuses on personal growth. The first 5 chapters or so are of his current life before he gets sent back.

SSS-Class Suicide Hunter. In case you want a darker story line. A man gains a skill at last but only after he dies. He realizes that he needs to die to keep using his skill. Yes, there's an initial revenge plot but that isn't the main storyline. His growth from constantly dying and him still placing value on each death (teaching him something) but also sadness (losing something) is very interesting.

are u stupid.. sorry if that was rude but like genuinely. did you even read the damn story? it was stated mc wasn’t upset that he got fired, he’s a dungeon master, he’s gonna be forced to make monsters and kill adventurers to live how he wants, what he’s doing isn’t that wrong you’re basically saying it’s okay for adventurers to kill monsters just because they want to prove their strong. Monster lives are still lives so if you’re mad about just adventures dying think about the monsters who die just as harshly, adventures choose that work if they die they die and that’s that.

I dropped this ages ago so I don't care anymore.