Manga where overpowered main character fights a demon

Question

In the beginning of the manga, it is apparent that our main character is overpowered. I do not remember if he was reincarnated but I would say that is a strong possibility. After getting a quest to subjugate a dungeon, he goes in there and some of the other parties that went in just hours before are already dead or dying. He makes it to the end of the dungeon and starts to fight the demon that is its boss; however he cannot defeat it because the demon is actually the dungeon itself. It is later revealed that the demon that was the dungeon was not actually its true body. But the demon that did have this power ends up coming to our main character because she needs his help.

The offer she gives him is that she will give him a dragon that she has tamed, but he does not want the dragon; rather, he gives the dragon's ownership to a female companion who is kind of weak. Later in the manga it turns out that the (blonde if I remember) hero is not doing his job; rather he requests women all the time and never actually does work. Because one of the females that our main character was with was summoned by this scumbag hero to be his, our main character goes and beats the crap out of him. While doing this our main character is disguised as the Demon Lord and while leaving with his female companion he put a spell on the hero that makes him feel pain whenever he touches a women.

Answer 1

I believe this is Nidome no Jinsei wo Isekai de, or Young Again in Another World.

The main character, Renya, is reincarnated into another world. He meets a pair of girls, who he helps out. Later he joins their party. For their first quest, they join a few other groups in clearing a dungeon. After they get there, one of the groups sneaks off to try to clear the dungeon alone to get the entire reward from the guild. After this was noticed, another group followed. Renya's group and the only other group to stay behind waited a few hours before heading in together.

They reach a room with a demon inside. After killing it, it is revealed that the demon was actually the entire room and not actually dead. Renya ends up beating him again, but everyone else was poisoned. Renya ends up making a deal with the demon to cure the others of poison. The dungeon core is supposed to be brought to the guild as proof the dungeon was cleared. The demon gives Renya rock that was the decoy core, explain that he, the demon, is the actual dungeon core.

After a while longer, Renya and his party take a quest to subjugate wyverns. Once they finish, a dragon appears, along with a demon girl. We find out that the girl is the true body of the demon from the first dungeon, and the dragon is her gift to Reyna to try and convince him to let her join the group. The dragon ends up being given to a girl who came with the party to gain the approval of her boyfriend's family.

Skipping ahead to the chapter called It seems like escape from the hero, Renya is disguised as the Demon King to rescue one of his companions from the blonde hero. During the escape, the hero was inflicted with 3 poisons. The first gives him a headache, nausea, and diarrhea when he touches a woman. The second causes the smell of a woman's sweat to burn his lungs. The final one cause his skin to burn when he touches a woman's bodily fluids.