"Don't cry. If you cry, you'll lose."
The Killer of the title. Ichi is a 22-year-old man-child who lives by himself in a big house. A childlike loner, he gets bullied around by almost everyone he meets and reacts by apologizing. He spends his days working at a metal factory and going to the red-light district. At night, he is a deadly assassin. Whenever pushed to the brink emotionally and past the Despair Event Horizon, he becomes a monster capable of tearing men to shreds. At first, he only kills when his mysterious guardian Jijii orders him to.
- Absurdly Sharp Blade: His boot razors, which he makes in the welding factory where he works.
- Almighty Janitor: Has unbelievable lower body strength and has spent quite some time practicing karate, yet he remains a white belt; this of course by his own choice due low self-esteem, Ichi thinks he doesn't deserve anything better than a beginner belt.
- Anti-Hero: Either an Unscrupulous Hero or a Nominal Hero, as he only kills under the orders of Jijii and his victims are usually the Yakuza or bullies who pick on him. That being said, he is the only character closest to the hero in this setting, and the most sympathetic.
- Anti-Villain: Type II.
- Axe-Crazy: Whenever he starts to cry, run as far as you can.
- Berserker Tears: Ichi cries when he's in his killing trance, since he both hates his own repressed ultra-violent tendencies and is simultaneously fueled by rage at the bullies who made his childhood a living hell.
- Beware the Quiet Ones: Certainly.
- Character Development: At the very end of the manga, although we don't get to see much of it, Ichi seems to have become more sociable and able to speak with girls normally, as seen in the hostess club; but he maintains his freaky smile and killer impulse.
- Charles Atlas Superpower: Extremely skilled in martial arts and has amazing lower body strength.
- Crouching Moron, Hidden Badass: A cowardly unassuming young man who can turn into a killing machine when pushed to the edge.
- Despair Event Horizon: He is pushed past it whenever someone attacks him in a way reminiscent of the bullies in his childhood.
- Morality Pet: His friendship with Kaneko's son Takeshi, who views him as "my wimpy big brother". Also Ichi's earlier friendship with the bullied kid, where he teaches the kid how to fight off the bullies.
- My God, What Have I Done?: His reaction after killing his girlfriend-prostitute by accident.
- Pet the Dog: Consoling the poor abused prostitute, and even giving her money so she can have her nose fixed. They even have a romantic moment and he promises to kill her abusive pimp for her...that ends badly.
- Nightmare Fuel Station Attendant: With puppy eyes and a sweet smile: "No. I didn't want to have sex. I wanted to rape her."
- Orgasmic Combat: Literally. The only way he can achieve an orgasm is through beating and killing others.
- Psychopathic Manchild: Ichi IS one of the top examples of this trope.
- The Un-Smile: His creepy nervous "smile".
- Unstoppable Rage: Whenever he goes into his killing trance.
- Woobie, Destroyer of Worlds: It's hard not to feel bad for this guy, especially since he knows he's insane and wants to be normal.
"Moral code, what's that?"Arguably the Villain Protagonist of this story. A Yakuza mobster who is equal parts sadist and masochist, he loves both receiving pain and dishing it out. He cuts, burns and pierces his body, and has twin friends who engage in S&M with him. His story begins when he finds out his boss and lover, Anjo, has gone missing. Kakihara is intrigued and goes in pursuit of Anjo's killer, but along the way takes over the gang. He eventually decides that Anjo's killer - Ichi - is the ultimate sadist he's been searching for.
- Berserk Button: Belittle his former boss or the Anjou Clan at your own risk.
- Big Bad: While he is the main point-of-view character in the manga, Kakihara is also the leader of the Yakuza that Ichi and Jijii are trying to take down, making him the leading antagonistic force.
- Cold-Blooded Torture: Oh, God. Since he's an extreme masochist, he is an expert at the human body and its physical limits, and applies this knowledge to his victims. His specialty is genital mutilation and keeping his victim conscious as long as possible.
- Combat Sadomasochist: He routinely tortures his enemies to death and enjoys every moment of their suffering. On the flip side, he also loves being hurt himself and had his Glasgow Grin given to him to enjoy the rush from the pain. (He's also this trope's current page illustration.)
- Dragon Ascendant: He was once a high ranked enforcer until his boss was killed and spends the manga taking over his gang and trying to get revenge.
- Glasgow Grin: Had Saburo give him one, back when they were in their previous gang, and the fallout from it scared him and his brother so badly that they never wanted to get on his bad side again.
- Good Scars, Evil Scars: He has a horizontal scar running across his cheeks and nose, a horizontal scar across his forehead, and a vertical scar that connects both over his left eye. In addition to a Glasgow Grin held together by piercings at the edge of his lips.
- Improbable Weapon User: He has a pack of sharp needles which he uses for both combat and torture.
- In Love with Your Carnage: He feels this way when seeing Ichi's killings.
- Nightmare Fetishist-Kakihara's hobbies are torturing people and being tortured.
- Sex Is Violence: "There's no love in your punches!"
JijiiThe self-appointed superhero of Shinjuku. He's an old police officer and Ichi's guardian, who has turned the man-child into an unstoppable killer through Mind Rape and brainwashing. Jijii is a mysterious old man (Jijii means "old guy") who has dedicated his entire life to balance out the good and evil in the city. Well, rather, the greater evil and the lesser evil.(Note, these tropes only apply for the movie.)
- Badass Grandpa: He always dresses very plainly so it's not visible, but he's RIPPED.
- Chronic Backstabbing Disorder: He betrayed almost every member of his own little gang.
- Cowboy Cop: He's a former cop whose goal is to eradicate the Yakuza from the city.
- Mind Rape: What he did to Ichi. No one deserves to have these horrendous "memories" implanted in them.
- Well-Intentioned Extremist: He's willing to go to its uttermost extreme.
- Younger Than He Looks: He looks like a geezer but he's actually on his late 30s... supposedly. This is thanks to Magic Plastic Surgery.
- Morality Pet: Strangely enough, Ichi is this to Kaneko. His company brings out Ichi's best sides, and Ichi views him as a cool big brother.
- Only Sane Man: When there's only him left in the gang, with Kakihara and Saburo.
- Professional Killer: A low-ranking hitman.
- Dumb Blonde: Appears to be this initially in the manga. She isn't.
- The Mole: Works for Jijii.
- Tyke Bomb: He ends up as Jijii's new assassin.
- When You Coming Home, Dad?: Used in the most tragic way.
- Woobie, Destroyer of Worlds: After his father dies and Jijii takes him in.
Jiro and Saburo
- Badass in a Nice Suit: In shiny white business suits, no less.
- Co-Dragons: They are Kakihara's most trusted enforcers and before Ichi can finally face Kakihara he has to kill both of them.
- Rape Is a Special Kind of Evil: They rape their way through the series. Almost every woman they're alone with is raped and brutalized by them.
- Theme Naming: Together with their late brother, Ichiro. Ichiro, Jiro and Saburo means "First Son", "Second Son" and "Third Son"