I think, I will drop this because I was fooled by the description. I thought he will betray humanity and kill them all but he still a nice guy. I don't know why he saved her. I mean killing her will protect humanity from their stupidity.
"Master of Martial Arts"
Leads by rushing in and throwing a blatantly telegraphed and overextended straight right punch.
The "martial arts" equivalent of a 3-year-old's crayon scribble.
I assume she's the "master of martial arts" the same way Saitama was better than Bang- she does seem to be naturally talented and has impressive raw power.
Why would he be? It's just a job for him, and the job isn't to even kill the heroes. It's to be a) a servant and b) to aim for a demon general title (for a promotion raise). He can satisfy those requirements just by winning and showing his incredible power. Even more so if he doesn't kill his enemies- it tells people he's so strong he can afford to look out for his opponents.