I would actually like to dig in to this with you, if you don't mind.
I don't think that "Genuinely regret that said theft was necessary," is at all what the angel is going for.
- Angels are probably deontologists, to the point that anyone who isn't Kant would consider insane. I think they entirely reject the concept of "necessary evils." You might have heard of the principal of double effect, but that has a bunch of necessary components which aren't present here. The act which causes good and bad effects can't be evil in and of itself, and theft qualifies as evil.
- The angel isn't asking for an apology, he is asking OL to repent for his sin. That means
- Acknowledging that what you did wasn't just wrong, it was a sin, caused by a moral flaw within you.
- You will strive to fix that flaw, so that you won't do it again in the future.
None of these apply to OL right now. I don't know if they can ever apply to him again, because of all the weirdness of orange enlightenment.
To use your example, I don't think the angel would consider killing someone in self defense to be a sin, and doing so would not require repentance.
TLDR: The repentance this angel is looking for requires rejecting/abhorring/denouncing whatever part of yourself led you to sin. OL can't do that ever again, because he has explicitly accepted all of his desires.