I'm looking for an action manga where the main character uses a knife to fight and is skilled at it.

Knife(dagger), not sword(katana).

Some examples are: Vinland saga, tokyo crazy paradise(tsukasa's chain weapon has a knife-like thing at the end), and Shingetsutan Tsukihime.

I'd like it if it had fight scenes in it that make you think "thats pretty badass"

ofc the longer the series the better.

________________
Feed your head.

Hmm, only ones that come to my mind are CAT main character and Eden's Kenji.

Though it's not manga you might wanna check Kara no Kyoukai (Novel). and there's also an anime version.

________________
Don't only look straight, look also to the sides, usually the essential isn't in front of you, but beside you.
-7

Crocodile Dundee

have you tried Melty blood? it is the sequel to Shingetsutan Tsukihime.


________________
"You shouldn't choose your path by your sins, Instead you should carry your sins depending on the path that you chose"

Scanlation has been down for a bit though.

MacGyver, sorry for the joke, but I think it's a lot better

________________
What I like in Trivial Pursuit style. Pick your category:

Try C.A.T. and Red Eyes. In Red Eyes the character doesn't strictly use a knife, but he sometimes only has a knife to use and that's all he needs. Red Eyes is one of the best military mangas ever, in my opinion.

________________

Monochrome Factor. Shounen Ai, BEWARE.

________________

Lots and lots of blood!