Our hero, a young samurai whose liege lord died in battle not long after Usagi entered his service. Now masterless, he walks the earth, occasionally hiring himself out as a bodyguard (hence the title), honing his skill as a warrior and meeting lots of interesting people.
Arbitrary Skepticism: Flip-flops a bit. He's pretty skeptical about the supernatural, though he's encountered more supernatural elements than any of the other characters (except Sasuke). He also strongly doubts Jei's claims of divine inspiration, and felt that the earthquake that occurred when Jei stuck the Sword of the Gods into the ground was 'coincidence'.
Beware the Nice Ones: A heroic version, since it's almost always the bad guys who try to take advantage.
Friend to All Children/Friend to All Living Things: Usagi always gets along famously with most of the children he interacts with, usually the kids of those he's a guest of for the night, and is unusually nice to the dino lizards that litter the setting.
Good Is Not Soft: Usagi is probably the nicest samurai ever. Many have mistaken this fact for weakness. Those people are dead now.
Hyper Awareness: A skill that Katsuichi-sensei physically beat into him and one that has saved Usagi's life many times. It can be over-sensitive and Usagi has a tendency to ignore correct hunches. Katsuichi-sensei also drew a distinction between this trope and Properly Paranoid.
Shout-Out: His name "Miyamoto Usagi" is one to the famed samurai/ronin/author of The Book of Five Rings, Miyamoto Musashi. He also often uses both swords at once during some fights, a style Musashi is famous for inventing/popularizing and something no other character in the comic does.
Victory Through Intimidation: Has ended more than one conflict with a Death Glare at his would-be opponent. Usually after slaying one or two of their comrades to add some weight to the silent threat.
Chief retainer to the young Lord Noriyuki; a controversial position for a woman, but one she's earned several times over. She and Usagi become friends early in the series after he helps her foil an assassination attempt on her master, and they gradually develop feelings for one another.
Celebrity Paradox: Although the idea for Tomoe's character was drawn from the historical female samurai Tomoe Gozen, Grasscutter actually includes a scene with the original Tomoe Gozen (in her elder years as a Buddhist nun.)
Naginatas Are Feminine: Tomoe began her career wielding a naginata. She had learned the sword from her swordmaster father but could not use them because she was a lady. By saving her lord from a ninja attack she was appointed "guardian of the heir" and was allowed to again wear her swords.
Ship Tease : With Usagi. By the time of "The Mother of Mountains", they became actual lovers, though Usagi's travels and Tomoe's upcoming arranged marriage have made the future of such a relationship iffy. .
You Go Girl : Due to the chauvinistic nature of the period, she's constantly having to prove her worth over and over.
Gen (Murakami GennosukÚ)
Usagi's less morally upright friend, a bounty hunter who cheats Usagi out of money the first few times they meet: which later becomes a running joke between them. He's more interested in preserving his gruff image than his samurai honor, but is not as callous as he pretends.
Ancestral Weapon: After the battle against Magistrate Oda's men, he discovers the swords he stole from Oda's armory were once his father's swords.
Luke, You Are My Father: Doesn't say it to Usagi's face, but shouts it after he leaves. Usagi hears something, but thinks he just imagined it.
IkÚ the farmer/General Ikeda
A general who joined an uprising against Lord Noriyuki's father, Lord Mataichi. When it failed, he and some of his soldiers went into hiding disguised as commoners, intending to take up arms again at a politically opportune moment; but when Mataichi died a few years later, Ikeda had become too attached to his farm and his peasant wife and children and decided to stay with them.He became an ally of Noriyuki after the latter saved his son Motokazu's life.
A wandering swordswoman of unparalleled skill, constantly pursued by bounty hunters since there's a hefty price on her head - she killed the yakuza boss who murdered her husband, and now his people want revenge. She saved Usagi's life once: if only because he'd paid for her drink earlier., but since she kills people so coldly he doesn't much like her.
Shout-Out: His name comes from a Kurosawa Film Nora Inu. His secret heroic bit is directly from Manga wrestler Tiger Mask.
The old hermit who taught Usagi more or less everything he knows: humility, compassion, thinking before he acted, and not least importantly his unusual style of swordsmanship. He's currently teaching Jotaro the same things.
Friendly Rivalry: In his later years, the only friend he still seems to have from his childhood is Isao, a fellow Old Master. They both trained at the same Dojo, both trying to surpass the other, and both saying they thought their opposite was better. After Katsuichi left Isao took over the dojo, and they still keep in touch.
The Rival: He had one in his youth named Toshi, he endured Toshi's jeers and mockery up until Toshi killed Katsuichi's lover and dueled him. Katsuichi killed him and left his school to become a hermit afterward.
The new head of the Geishu clan following the death of his father, Lord Mataichi. At the beginning of the series Noriyuki is about ten; he's one of the few characters to have visibly aged, though only by a couple of years.
A skilled fox ronin, Sasuke is a demon slayer and has devoted his life to hunting them.
Determinator: When he's set upon a target, he travels miles to get to it. Whenever he expends too much energy, he's left an old man, but the spirit who grants him his powers continues to order him to the next definition, and Sasuke goes without complaint.
Did You Just Punch Out Cthulhu?: To almost every other character in the series, supernatural monsters and wizards are rare and terrible things. But it's starting to look like Sasuke is the reason they're rare.
Enemy Mine: They ally with Usagi to face Lord Tamakuro. They then declare that they have no further alliance with Usagi.
We Have Reserves: Usagi and his companions have killed a lot, to say nothing of those lost to Lord Tamakuro in The Dragon Bellow Conspiracy. By the end of Grasscutter II it's clear that they cannot continue to sustain such terrible losses, leading Chizu to question their continued association with Bad Boss Hikiji.
Team Mom: When she becomes head of the clan. Everyone's not pleased.
Trauma Conga Line: When Kagemaru pulls his coup, she has all her friends and allies turned against her, she's cut, poisoned, and dropped into a moat. Kimi finds her sick, freezing and bleeding on the side of a building later on and a barely coherent Chizu must accept that she's now a fugitive.
He Who Must Not Be Seen: As a Japanese lord he doesn't need to be seen to be influential. He's the only human character in a world of animal people. When he's shown in Usagi's village, he's wearing a battle mask.
Enemy Mine: Hebi sent the Neko ninja with Usagi and Tomoe to stop a lord who was planning to betray Hikiji, and had stockpiled guns. Noriyuki tells him that he only did it to serve his interests. Hebi merely states that they should be grateful that they stood together against this threat.
Unwitting Pawn: As smart as Hebi is, he's clueless to the Neko Ninja's power struggle, and is manipulated into ousting Chizu by Kagemaru.
What Measure Is a Non-Human?: Hebi is one of the cruelest and most inhuman characters, and coincidentally also one of the scariest-looking and least human.
Jei-san the Blade of the Gods
One of Usagi's deadliest enemies. In his first appearance he is showed as a crazy killer who think himself as an emissary of the gods in a mission to clean the world from the evil by any means needed; but with each appearance, although it's never confirmed that he is the blade of the gods, it's made more clearly that he isn't just a normal person, neither.
Blue and Orange Morality: Jei is everything he claims to be, a servant of the Gods sent to cleanse the world of evil. The only problem is that Jei and the Gods he serves have a view of Good that everyone else would describe as pure undiluted Evil.
Dark Is Evil: He doesn't just wear black clothes; whenever he put the hands in a blade it immediately turns black.
Fate Worse than Death: being stabbed by his spear—or later, sword—is shown to be agonizing, and it's implied that if it happens to you your soul is destroyed.
Slasher Smile: And when he starts chuckling it's too late to run.
The Virus: "Jei-san" is actually a spirit/demon who uses people as hosts.
Jei-San's "niece", who he spared after killing the thieves who killed her grandpa because she was "innocent". Having nowhere else to go, she started following him. She was originally supposed to become Jei's new host, but the author felt uncomfortable so he created Inazuma.
Usagi's beloved lord, defeated by Lord Hikiji's forces. The war was caused by Hikiji sending the Neko Ninja to murder his wife and child. Usagi personally decapitates his lord's body to ensure his head isn't used as a trophy.
Two monkeys, husband and wife, who have an amazing - and totally coincidental - tendency to travel to whatever area Usagi is in: they're routinely seen in any scene set on a road. They play a minor role in one story in Book 3, and come within a hair of being the victim of a villain in Book 22, but ordinarily they have no lines and are simply seen passing by. They refer to each other as "husband" and "wife".