I just spent the last three days reading Noblesse and now that I'm caught up, I don't know...

Black butler? I think you've already seen/read it.

Yeah, I have, but thanks anyway.

maybe makai ouji? or there's rust blaster by same author of black butler

Hi! What about "Royal Servant"? You can find it here, I think it's really nice!

Thanks, I'll check it out!

Thank you, I'll give it a shot!

TAL is another good, action-packed webtoon ^^

Sidekicks might be for you then! (superheroes, action, comedy) http://www.webtoons.com/en/super-hero/sidekicks/list?title_no=92
There is also this little side story to Noblesse: http://www.webtoons.com/en/fantasy/noblesse-spin-off/list?title_no=608
Or Lessa: http://www.webtoons.com/en/fantasy/lessa/list?title_no=89 and http://www.webtoons.com/en/fantasy/lessa-2/list?title_no=507
Or as already suggested TAL: http://www.mangago.zone/read-manga/tal/
Or Hong-do: http://www.mangago.zone/read-manga/hongdo/?av=1 (up to ch. 31, for the rest you have to pay here ->) http://spottoon.com/book/30/HONG_DO

Okay, it's late here, sorry... I didn't read your question completely... (￣∇￣")

So, Hong-do is def. not what you're looking for, Lessa probable neither. I still recommend the side story, of course, and TAL. There's this sidekick/master relationship which you might like, in Sidekicks, but the MC is a girl. Still, if you liked Noblesse, I think you might like that one too!

Wow, thanks for all your suggestions!!