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: An extreme example of an Unscrupulous Hero at best, since 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.
- Expository Hair Style Change: In the epilogue set three years later, Ichi has grown his hair out into a longer, flared out style; highlighting his more sociable and confident nature, but also foils Takeshi's hairstyle change.
- Fake Memories: It's implied throughout the manga given Jijii's better memory of Ichi's past than Ichi himself, but Jiiji would manipulate Ichi's memories and Ichi's imagination would expand and fill in details after being prompted, to the point that it's unclear how the events actually happened or if the events even happened at all, and this would be his tactic when killing; associating his memories with his targets.
- 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.
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.
- Asshole Victim: He has his penis and arm sliced off by Ichi and then falls to his death. While that is a rather brutal fate, Kakihara himself was so subhuman that there's hardly anyone who would shed a tear for such a despicable monster.
- 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.)
- Deadpan Snarker: He just as sarcastic as he is sadistic.
- 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.
- Hate Sink: He is, without a doubt, the most disgusting and vile example of this trope ever written.
- 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.
- The Sociopath: As you can already tell, Kakihara a depraved monster with no morals or humanity.
- Sex Is Violence: "There's no love in your punches!"
- Too Kinky to Torture: That is untill Ichi slices his cock in half.
The 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.)
- 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.
- Everyone Calls Him "Barkeep": His real name is never given and is only ever called "Jijii."
- Mind Rape: What he did to Ichi. No one deserves to have these horrendous "memories" implanted in them. In the final chapter when Ichi runs into Takeshi, Takeshi has no memory of Ichi; implying Jijii is using the same tactics on Takeshi.
- 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.
- An Arm and a Leg: While being interrogated by Jiro, he physically rips out both of his arms; simply to see if he could.
- Dropped a Bridge on Him: Ichi shows up and kills Jiro, saving Noboru, but then immediately turns around and kills Noboru. It's revealed Jijii orchestrated it, as Ichi and Jijii's gang have never met, and had given Noboru as one of Ichi's targets.
- Half the Man He Used to Be: In a metaphorical sense, Kakihara splices his genitals while being interrogated.
- Last of His Kind: He's the last member of Jijii's gang to get killed.
- No One Sees the Boss: He, Ryou, and Inoue have never met Ichi, only cleaning up after him. Noboru is the only one who meets Ichi, but since Ichi has never met him and Jijii used his master manipulation abilities, he has Ichi off Noboru.
- Those Three Guys: He, Ryou, and Inoue are the members of Jijii's gang, but the three of them are really only in charge of cleaning up after Ichi and are oftentimes forced to just stay back in their hideout.
- Aw, Look! They Really Do Love Each Other: It's no secret that Miyu adores Ryou, however, he seems to just be using her to make money. When they're both abducted by Kakihara, Ryou reveals he really does care about her and his final words are telling her sorry.
- But Not Too Foreign: He's Chinese.
- Half the Man He Used to Be: Metaphorically, Jiro punches and then Saburo slices his genitals, mocking him by saying "how can you be a pimp without your money maker?"
- Lovable Sex Maniac: His main source of income is he's a pimp, having about twenty or so girls under his belt, one being his girlfriend. He reveals he does this as a means to love girls that find themselves incapable of being loved
- Manipulative Bastard: Ryou has Miyu deposit her earnings in their shared bank account in hopes of opening a tea shop, Noboru believes it's just Ryou is conning her out of her money and he essentially admits to it. Then you learn he actually cares.
- Those Three Guys
- Together in Death: He and Miyu-Miyu, his girlfriend and one of the girls he pimps, die shortly after each other at the hands of Jiro and Saburo.
- Addled Addict: What ultimately leads to his end was his addiction to cocaine, he enters withdraw and tells his provider, who's being used by Kakihara, the address of their gang's hideout to get his fix.
- Those Three Guys
- Magic Plastic Surgery: He went under the knife, and the result is good enough to fool his old fellow gangsters.
- The Mole: Inoue used to be part of the Anjou clan before being excommunicated, he used this connection to plant bugs throughout the Yakuza Mansion so Jijii and his gang could listen in and spy.
- You Don't Look Like You: He got plastic surgery done on his face after being excommunicated from the Anjou clan so he could stay in Shinjuku, when Kakihara's gang catches him, all the members say he doesn't look anything like how he used to.
- We Hardly Knew Ye: He is the first of Jijii's gang to die, being killed off about a third of the way through the manga.
- Foil: To Ichi in their natural personalities, Ichi is a coward and timid while Kaneko carries himself with strong, self-assured confidence; when working, Ichi is calm and collected while Kaneko shakes in genuine fear, even tripping as soon as he enters an apartment when searching for Ichi in the final volume and dropping his gun when Karen unexpectedly shows up and thinks it's Ichi.
- If I Do Not Return: He asks Ichi to look after Takeshi in case anything happens to him. Ichi doesn't understand what he means until he realizes Kaneko is one of his targets that he has to kill.
- Last Request: His last words are tearfully asking Ichi to take care of Takeshi for him.
- 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.
- Tears of Blood: Has these when he's dying and asking Ichi to look after his son.
- Dumb Blonde: Appears to be this initially in the manga. She isn't.
- The Mole: Works for Jijii.
- Blood-Splattered Innocents: In the epilogue, Takeshi clumsily falls out of an alleyway, holding a bloodstained knife with blood stains on his face; implying he has recently begun his job as Jijii's latest killing machine.
- Character Tic: For a good portion of his appearances, he always has his hand covering his forehead. It's to hide that his bullies cut some of his bangs, leaving them uneven.
- Expository Hair Style Change: In the epilogue, he has grown his hair out in a style very similar to the one Ichi currently has; but it's moreso to display that he is being subjected to what Ichi experienced.
- Fake Memories: As Jijii did with Ichi prior, it's implied he's implanting fake memories into Takeshi, such as he doesn't remember Ichi when they run into each other at the end of the manga.
- Sinister Switchblade: He uses a switchblade as Jijii's assassin.
- 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"