Bruhhhhh. What humanity are you talking about? Who melts another human being for being obstacle? She did tried to melt him. It's okay to kill if it's for survival.
Whats all this stuff about people having unique powers? Doesn't that completely contradict all the juts folk from earlier who could do a fair bit of different stuff? Is this series just going to change its rules every arc?
This dumbas.... is he seriously not giving thought to the danger they could pose to him if he lets them go? Not even talking about the need to interrogate them! Best line of action would be to kill the madman and reatrain the other, but even if he can't kill he should at the very least restrain and kidnap both of them