It wasn't properly explained in the manhwa but he often let himself be punched in that body bcs: 1. Sergeant Kang Hajeong's body is too weak (he's slowly trying to get in shape w/ the help of Han byeongeun), 2. He will use it as evidence to report the abuse; he has done this before to the Esper from the team he used to belong although not shown in the manhwa (this happened when he was admitted to the hospital).
Also, yeah it's a dream; he suspects it's bcs he made contact with Kim Muhyeok's wavelength before
Like a previous comment said the manhwa isn't as clear as the novel about MC and MLs guiding dynamic before MC died. They'd never been intimate in that way before. Most of their guiding was minor physical guiding (ie hand holding, sometimes cuddling when the ML initiated it, etc) or "radiation" (I think that's what they called it) guiding. Radiation guiding is like basically just being near the guide and the guide gives off waves that just get absorbed by the esper.
Also mentioned, MC takes punches with a purpose. The same is also true that this body is incredibly weak. While I think the manhwa does a good job showing this body is weaker than MCs og body I don't think it's good at showing just how weak he is rn. MC often mentions in the novel that it hurts this body to just exist.
SOME MINOR SPOILERS BELOW
If this follows the novel then these two aren't going to fuck until the side stories and that'll be their first time as a whole. ML and MC are both virgins.
hope that was only a dream and they weren't that intimate before he died. also why must we turn a sergeant into a damsel in distress who needs saving from a punch?