Henkyou-gurashi no Maou, Tensei Shite Saikyou no Majutsushi ni Naru - Vol. 3 Ch. 11 - Former Demon Lord, Fighting the House Tutor

[MangaDex]

 

[Aoitenshi]

I was half expecting the bat would just ignite with that flame rune, but oh well.

 

[xXPenisXx]

I really, really like him going "Yeah, my brother said some stupid shit to me and we fought. Brothers do that."

 

[Shendelred]

Man... this princess is so annoying. They almost annihilated by this scumbag tutor if the MC hadn't come on time, but she kept insisting on not killing him... Now, MC's brother is in danger because of this saint-hearted princess. I understand not killing him (for the info about this Elysium) if they can hold back this scumbag tutor without the help of the MC, but they can't even touch him with their attacks... I really hate this kind of saint-hearted trope characters that can't even kill ants

 

[SimonTheEcho]

Man... this princess is so annoying. They almost annihilated by this scumbag tutor if the MC hadn't come on time, but she kept insisting on not killing him... Now, MC's brother is in danger because of this saint-hearted princess. I understand not killing him (for the info about this Elysium) if they can hold back this scumbag tutor without the help of the MC, but they can't even touch him with their attacks... I really hate this kind of saint-hearted trope characters that can't even kill ants

I think it's more like she doesn't want him having a noble's blood on his hands. In some cases, killing a noble, self defence or otherwise, can get you executed or targeted by said noble's family. Not to mention that he may not be able to attend the magic school, or whatever it's called, or become her knight, both of which she seems to want him to do.