well, let’s remember that he kick the ass off some sort of arch-devil : he’s powerful enough to brush off any bad scheme the bad guy will try to pull… so what if he let his idiotic, power hungry brother live ?
@Woodchipper well, at least, Star Martial God Technique is not on the same level than Peerless Martial God in the concept of "you have the audacity of not groveling before my family and dare to fight back when I harass you for no reason ?"
Is it me or does the writer of this manga change along the way ? We got from a super-magician with extended knowledge and cheat abilities that getting along with a cute "teacher" and pwned a S-rank monster with a single strike, to some average caster who had a hard time slaying some random daemon ?