What does that end part mean when Kuro is by himself and says"there you are"?!!!?!?!?!?!?!...

As far as I understand it's another cat monster he was previously fighting (He mentions another cat monster, a fight and that they can't get kill each others).

Another cat monster could be a possibility. I personally thought that it was Shouei's senpai that we see near the end there. It seems they met each other during Kuro's disappearance.

I was thinking the same thing. And the way senpai was built I felt like he could handle Kuro!