Thanks for the chapter!
Now is the Demon King a lolibaba or got selected because inherited position from previous holder who died recently or some special ritual or whatever declared her Demon King? In any case, this is going to be a short series since the MC is going to be smothered by the Demon King's chest. Also, that's not warmth he's feeling but his lungs burning for oxygen and hallucinating due to lack of air. Hope they're going to explain what entering the dungeons of successive Demon Kings is for and why want him to do it.