I'm looking for manga with interesting, unusual main characters. Some that come to mind are Ichi in Ichi the Killer and Kano in Freesia, and perhaps Nakamura in Aku no Hana (I feel like she borders more on normal yandere).

I prefer no fantasy and no ecchi, but these are not complete dealbreakers. Complete series only please.

All the characters in your examples are pretty violent, though. Are you looking only for the killer types, or would others be okay? For now I'll recommend the ones with violent/murderous/otherwise immoral MC's:

Blue Heaven
Jiraishin -- But not a villain protagonist
Girl May Kill - Female MC
The World Is Mine is supposed to be like Ichi, but I haven't actually read this.
Ayeshah's Secret
Innocent (SAKAMOTO Shinichi) and its sequel
MW
Trick Ster
Wolf & Mary

Hellsing - Maybe? I found the cast unusual for that kind of series (mostly because the protagonists were just as bad as the antagonists), but they aren't really all that different from standard villain protagonists.

Dendrobates - Another 'maybe.' I find his unwavering life philosophy interesting, but he himself is a fairly standard, if cool, anti-hero.

Other personality types are totally welcome, I just could only think of violent examples 🙂 Thanks for the recommendations.

But now that I think about it, most manga with non-murderous unusual MC's tend to be fantasy/supernatural 😲 I'll mention some just in case, not sure whether you'll like them:

Chimoguri Ringo to Kingyobachi Otoko and its sequel + other titles from this mangaka.
Discommunication Seireihen
Sakai no Musume - Cat in the Car
Sayonara Minasan
Cuticle Tantei Inaba
The Voynich Hotel and anything else by the same author.
Umbrella Sword
Pure Trance
Mononoke Soushi - I'm not sure about unique...perhaps 'cool' would be a better descriptor.
Dainippon Tengutou Ekotoba

+ Tic Nee-san -- Well, if completely wacko=unique. Quite funny, and no fantasy, either. Same goes for Dadadadan., Zai x 10 and Danshi Koukousei no Nichijou.

Thanks, I'll check them out 🙂

I just started reading kaguya-sama wa kokurasetai and I think the main characters are really unique