Okay then, fighting manga with flawed heroes and grey morality.
Übel Blatt - one of my favourite antiheroes. He's also got a badass sword
A Fairytale for the Demon Lord - perhaps, I've only read six chapters yet
Ajin - it's basically about zombies. Has the grey morality thing down. There's also some fighting (for one's life)
Aletheia - that mc... I can't tell you why he's interesting without spoiling you a bit, but since it's still got just a few chapters out, it's pretty quick to read. The story''s moving kind of slowly though
Be Heun - a retired badass war hero, if I remember correctly. not 100% sure if this is what you seek
Black Haze - okay, this is just
Good (attention to the italics and capital letter) even though it's not exactly what you've asked, it's got some fighting and the mc is no saint. he's also very pragmatic
Chang Ge Xing - sorry I keep giving you strategy recs, but this is just so surprisingly good
Godly Bells - mc seems kind of wimpy at first but turns out to be very interesting
Gun x Clover high-ranked in disguise. has dark past, wants revenge, etc etc
In Full Bloom (YON Jae-Won) One ruler, one schemer, and... one assassin. Need. I. Say. More!?
Itsuwaribito Utsuho he's a liar with heart of gold. Also pretty crafty
Jormungand and probably
Black Lagoon but I prefer Jonah to Rock
Waltz The mc's an assassin and pretty flawed
Vinland Saga Goddammit read it NOW it's got BLOOD, it's got REVENGE, it's got a FLAWED MC, it's got EVERYTHING
Yongbyeong Maluhan probably
Ares set during wartime if I'm not wrong, so lots of grey morality
maybe (probably) not all of them are what you're looking for, but most of them are really good
edit: also seconding 1/2 prince, eclipse hunter, sun knight and girls of the wild's also has a lot of fighting
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