Of course the slime turns into a fucking little girl, the author is rEaLlY cReAtIvE.
Also the accident of lime eating the stone is so unnatural, why did he left the giant ass stone that's dangerous just lying about in his room? Why didn't he just put it in his dimensional storage or whatever that he have? This would feel much more natural if he just fed lime the stone (thats what he's going to do anyway) intentionally and then woke up seeing that lime have turned into a human form