The obvious answer is Spider-Man. He's my favorite fictional character, period. No one else comes close. But, like last week, I talked all about him last fall, and where's the fun in just throwing out the link to that post? So I'm going to talk about a guy I really like, but almost never talk about. Since this is going to be about manga, remember to read right to left, please.
So he has some grudges, and they're justified, he just happened to go after one guy who a) recognizes the revolution hasn't ended and works to improve things his own way, and b) hadn't taken any benefits or perks from his service. The fight ends - though Sanosuke lost convincingly - and he resolves to stick around and see if Kenshin is who he appears to be, or if this is just another trick. They pretty quickly become friends, since Kenshin isn't the sort to hold grudges, and Sanosuke has Kenshin's back through pretty much the remaining 26 volumes of the series. Except for that stretch where Kenshin kind of gave up, and Sano left for awhile in frustration and disgust. But he came back for his friends when they needed him!
They are very different characters, though. Sano is blunt, direct, and open. Whatever he's feeling, you'll know it, whether because he tells you, or because he slugged you in the face. It doesn't matter who you are, he's not going to stand on ceremony. There are a lot of times I'd like to be more like that. Just tell people what I think of them and go forward from there. Like Kenshin, he wants to try and make things better, but whereas Kenshin is more concerned with protecting the weak, and will accomplish that without violence if possible, Sanosuke is more inclined to just go beat the hell out of the bad guys. Like the picture below, those poor dopes are part of a gang of 200 guys serving under a disgraced sumo wrestler/Yakuza who is helping a crooked government official (who happens to be his uncle, so nepotism) to corner the silk trade in a small village, garnering huge profits for themselves, while putting a chokehold on the locals. Kenshin could have wrecked that official's plans with one word to any number of people in the government who owe him their lives. But he was in the throes of depression, and Sano was in a foul mood, so things were resolved with beatings. Which is more fun, anyway.
Most of the characters in Rurouni Kenshin are older than Sanosuke, who is 19 went the series starts. They're contemporaries of Kenshin (who is 28 or 29 by that time). People who fought in the war, rather than serving as aides or assistants. People who had extensive training and survived dozens of battles against opponents who also had extensive training. Sano doesn't have that advantage, he's starting from behind and trying to catch up, but that never deters him. He's almost constantly underestimated. Kenshin thought he could beat him with one hit. Shinjiko felt he was stuck fighting 2nd-rate goods because he had to leave Kenshin to his boss, Shinomori Aoshi. Saito dismisses Sanosuke for a long period of time (and never gives him credit to his face, even if he admits to Kenshin he knows Sano is reliable). Shishio's right-hand guy, Hoji, dismisses Sano as a "tagalong", right before Sanosuke destroys their ironclad.
But it never stops him. Sure, sometimes Sano gets his ass beat, but he always goes down swinging. His fighting style pretty much mirrors his personality: He doesn't know or care a thing about defense. He'll take your best shot, then deliver his own. This isn't necessarily a smart approach - even when he wins, he's almost as beat to hell as his opponent - but I still like it. You don't have to be versed is some otherworldly sword art, if you can take the pain and keep going, you've got a chance. He's usually an underdog, but that's fine, the supporting characters usually are in shonen manga. The main characters are almost always going to win, and even if they do lose, it's always to some high level opponent. Kenshin doesn't have really have an equivalent loss to those two times Spider-Man lost to Stilt-Man, you know.