@HDMI1 what you mean makes sense, but not that much in this situation and cast. MC knows well that he's something like a god in this world, only speaking bout his abilities. This "assasin" had shown nothing of the sort that would indicate her as playfull, even more obvious when she ran away...
As always, holding back, seeing your loved ones die so that you can then stop holding back. They wont find out that your OP when they already dead, smart.
Shit, her reasoning was legit. It's really hard to swallow, but it's how it is. The only other option would have been to search for a solution happy go lucky together, which is kinda risky. She chose the for herself best acquire able path... good for the drama.