When the main character of a story is a bit morally ambiguous and lacks typical heroic traits, that makes them an antihero, and the world of anime is filled with them. Antiheroes come in all shapes and sizes, with differing levels of moral ambiguity. Some just have a few morally gray incidents here and there, some just have a really exaggerated sense of justice, and others are practically villains who just happen to be the center of the story.
That doesn't mean that these are the characters that anime fans are meant to root against. In fact, some fans prefer them to typical idealized heroes simply because they come off as slightly more human with their flaws.
10 Hellsing: Alucard Is Count Dracula Himself
One thing that gives away the fact that Alucard isn't a typical hero is that he's an incarnation of Count Dracula, as his name suggests. He is a vampire hunter who fights against his own kind, due to serving the Hellsing family.
Arrogant and remorseless, it's been noted that he likes to break his opponents before killing them. He also has mixed views on humans, as he seems to envy them, but also shows the desire to be defeated by one. He opposes vampires going around killing without mercy, although it's more due to the lack of honor than a regard human lives.
9 Space Dandy: Dandy Is A Delinquent, Complete With The Pompadour
Dandy is something of a mix between an alien hunter and a delinquent, something his beloved pompadour makes immediately clear. He can be callous and neglect the needs and feelings of those around him, outright insulting them out loud. He also tends to be a hypocrite, claiming to dislike things that he indulges in, but claims this is more due to bad memory.
That said, he does appear to have a good heart deep down. Sometimes, he'll even show himself to be nicer than he claims to be. For example, he claims to dislike children but seems to get along with them.
8 Captain Harlock: Captain Harlock Won't Smile, But He Will Cry
A classic anime character, Captain Harlock is famous for saying that he fights for something he keeps hidden in his heart and not for anyone's sake. He's a pirate but became one out of disgust from decadent governments and oppressive powers. He rarely smiles but isn't against breaking out into tears when the situation calls for it.
Captain Harlock has appeared in different stories over the years, each within their own continuities, meaning his personality might change between the different versions. For example, he can go from rather sexist to being outright chivalrous.
7 Berserk: Guts Wants Revenge On Griffith
There is a reason that Guts is known as the "Hundred Man Slayer" and "The Black Swordsman." Already having a dark past before the events of the eclipse, notably being found as a baby near his mother's hanged corpse, he is introduced as a mysterious wanderer with a fate tied to his former friend Griffith, a character he really wants to get revenge on.
Despite appearances, he has a good heart deep down, his usual indifference to others is something of an act, and, while he can be a powerful threat in battle, he at least doesn't like to involve innocent bystanders.
6 Death Note: Light Yagami Had A God Complex Before He Had The Power To Kill
Light is simply one of those protagonists who would be the villain if the story wasn't more or less told from his perspective. A talented student, Light's main issue in life is that he has something of a God complex, which takes a turn for the worse when a Shinigami named Ryuk drops the mysterious yet powerful Death Note. Now, Light has the power to choose who gets to die just by writing their name down in the book.
Generally, as a character who appears in different media, Light can be more sympathetic depending on the story, sometimes wanting to use this power for good, but, given that killing others is kind of his schtick, it's hard for him not to come off as an antihero.
5 Attack On Titan: Eren Yeager Is Practically Powered By Hate
Eren is a bit of an idealist and wants good things for humanity, giving him some elements of a typical hero, but his hatred for the Titans really helps him come off as an antihero in his own way, too. It also helps that he's effectively powered by hatred, which is what allows him to transform into a Titan.
On a related note, he also doesn't have the best reputation outside of Paradis Island, with people thinking he wants to destroy the world, not that he wouldn't necessarily be against the idea of destroying life outside of Paradis Island, either.
4 Cowboy Bebop: Spike Spiegel Is A Bounty Hunter With A Past
Spike is a bounty hunter with a colorful résumé, having spent time as an assassin, a gangster, and even a martial artist, not to mention the time he faked his death. He doesn't take things too seriously, with a lazy, easy-going personality, which can be a bit surprising considering his line of work, although this seems to come from years of heartbreak.
Added to this, he's not necessarily a nice character, as he initially doesn't mind innocent bystanders getting hurt, but this changes over time.
3 Lupin III: Lupin Is A Gentleman Thief Just Like The Original
Arsène Lupin III is the grandson of the famous gentleman thief, Arsène Lupin, and naturally is a criminal himself. In fact, he's considered one of the top thieves, if not the top thief, in the world.
Despite this, he and his allies often stop other criminals from taking over the world, but they still act out of self-interest more often than not. On the other hand, Lupin III does tend to be less villainous in anime adaptations when compared to the original manga.
2 One-Punch Man: Saitama Just Wants A Good Challenge
One of Saitama's main motivations is to find an opponent that is worth the challenge. In other words, a target that won't go down after just one punch. In fact, because of his immense power, he's seemed to have grown bored, lazy, and cynical when it comes to the hero business.
He does seem to enjoy saving the day, saves his power for the villains, and does try to help other heroes get respect, even at his own expense, showing he has a good heart.
1 One Piece: Luffy & The Straw Hat Pirates Is A Team Of Antiheroes
Luffy is a study in contrasts. He's a pirate and a criminal, but really only antagonizes characters who deserve it. He values his friends and thinks of them as his greatest assets, but doesn't mind the occasional collateral damage to public property or even his enemies. He also has some respect for more traditional heroes, but wouldn't want to be one out of the expectations, like having to do things such as share meat.
All in all, the other Straw Hat Pirates all have shades of being antiheroes, with some even originally being introduced as straight villains before joining up with Luffy.