A boy raised among the elite of No. 6, only to be stripped of his privileges after giving shelter to Nezumi, a fugitive. He is unfailingly polite and idealistic and refuses to give up on saving the people of No. 6.
- Adorkable: Often.
- Adaptation Dye-Job: His eyes were violet in the novels as opposed to the red in the anime and manga.
- Back from the Dead: Only in the anime
- Ambiguously Bi: Subverted. Even though Shion promises to have sex with Safu after her two-year study program when she asks him to, the author makes it clear in the novels that he considers her nothing more than a good friend, and that his affections really lie with Nezumi.
- Badass Adorable: He seems all cute and innocent on the outside, but mess with someone he cares about, specifically Nezumi, and get ready for the beatdown of your life.
- Berserk Button: Don't insult or even attempt to harm Nezumi in Shion's presence. It may very well be the last thing you do.
- Bishōnen: Not on the same level as Nezumi, but he still qualifies.
- Brainy Brunette: Before the wasp, anyway. He's definitely still brainy though.
- Break the Cutie: The series tries hard, but Shion is too much of a Pollyanna to give in. It does finally hit him, and hard on the Correctional Facility, but even then and probably thanks to his Cloudcuckoolander tendencies he manages to go back to his old self with few negative repercussions.
- Chastity Couple: Played straight in the anime and manga where his and Nezumi's relationship is not portrayed as overtly sexual, but averted in the original light novels, in which they share a bed and it's a foregone conclusion that they're having sex regularly.
- Child Prodigy: Before meeting Nezumi, Shion was an ecology major in the city's gifted program with enough practical knowledge to safely suture wounds at the age of twelve.
- Did Not Get the Guy or the Girl: Ultimately subverted. Not only does Nezumi leave him behind when the walls around No. 6 come down, his Het Option Safu (notwithstanding his disinterest in her as a partner) Ascends to a Higher Plane of Existence. However, Nezumi and Shion do become the Official Couple, and Nezumi promises to come back to Shion eventually at the end of both the novels and the anime.
- Disappeared Dad: Mentioned only in the novels. His mother claims he was a borderline alcoholic who slept around and spent recklessly.
- Beyond gives more information. Also, Nezumi meets him.
- Disease Bleach: The reason for his white hair.
- Even the Guys Want Him: Nezumi, of course, but he was also hit on by a greasy old corpse-collector, with promises of meat and drink, no less.
- Friend to All Living Things: He took in the fugitive Nezumi and treated his gunshot wound when they were children, dooming his bright future in the process. Years later, Nezumi's mice take a liking to him (he even gives them names), he reads to the neighboring kids in the Western Block, he gets along with Dogkeeper and their dogs, and Rikiga even calls him an "angel" at one point.
- And at the end of the anime, he even adopts the ridiculously cute baby he saved two episodes earlier.
- Genius Ditz : Even though Shion is naive and lacks a sense of self-preservation, he was ranked the highest in the city's intelligence test when he was just two-years-old.
- Headbutt Thermometer: How he checks Nezumi's temperature when they first meet.
- Heroic Safe Mode: In the manga, seeing Nezumi get shot for him almost results in a complete breakdown until he manages to get his logical side to take over. Played with though in that this safe mode comes dangerously close to turning into his Yandere mode, to a point that it actually unsettles Inukashi and Rikiga.
- Homoerotic Subtext: With Nezumi. Invoked deliberately.
- Incompatible Orientation: He never gets the chance to good on his promise to have sex with Safu, but that works out well enough for him considering he didn't want to in the first place.
- Locked into Strangeness: In roughly the span of a few hours or days after the wasp fails to emerge and kill him, his hair turns completely white and his eyes change color — violet in the novels, red in the manga/anime. He also gains a red snake-like scar curling around his body from his cheek to ankle. He's understandably a little freaked out by both changes and while he adapts quickly, he remains somewhat self-conscious about the "snake"
- Love at First Sight: While it's never outright stated, it's pretty obvious that Shion fell for Nezumi the moment they met. Karan even mentions at one point that Shion kept mumbling Nezumi's name as though it belonged to someone who'd stolen his heart.
- Love Makes You Crazy: Downplayed. When Nezumi is threatened, sweet, naive Shion reacts in two ways: All-out rage or cold, rational murderousness.
- My God, What Have I Done?: He usually reacts this way whenever he comes out of his Yandere outbursts. Has a much more serious breakdown after killing a man who hurt Nezumi, but due to the extremely critical circumstances he manages to regain his cool rather quickly.
- Or not so quickly in manga and novel where he outright attempts to kill himself and only Nezumi breaking down and crying for him was able to snap him out of it.
- Momma's Boy: Well, his mom is Karan. Shion was raised solely by his mother and both of them are (happily) devoted to one another. That doesn't mean he is dependent on her, though, and handles being away from her for most of the story just fine.
- Morality Pet: For Nezumi. An unusual example in that he struggles with moral issues himself — in fact, he becomes more willing to hurt others through his association with Nezumi, and the latter ends up having to serve as this for him in a sort of reverse Morality Pet effect.
- Meaningful Name: "Shion" is a flower (specifically, a type of aster) with medicinal value. The flower also means "I will remember you" or simply "remembrance" in Japanese tradition which could allude to the ending.
- Nice Guy: To a fault.
- Beware the Nice Ones: But there's a reason we keep saying not to screw with Nezumi.
- Official Couple: With Nezumi by the end.
- Please Don't Leave Me: Said almost word for word when Nezumi is about to leave No.6.
- Please Wake Up: After escaping the correctional facility and finding a doctor to help Nezumi.
- The Pollyanna: No matter how grave the situation, Shion can very nearly always find the silver-lining, even after being relegated to the equivalent of the slums for No.6, becoming targeted by the city, losing his mother and best friend, and discovering a massive government conspiracy. He finally breaks when Nezumi is shot, and it's horrifying, but even then he manages to snap back at his usual self fairly quickly.
- Red Eyes, Take Warning: In the anime and manga. Averted most of the time. Threaten Nezumi, however, and see what happens.
- O.O.C. Is Serious Business: It only happens two or three times in the entire story but anytime Shion is not his usual sweet, caring self it's outright terrifying.◊
- Single-Target Sexuality: While the related materials do set up Safu as a nominal rival for Shion's affections, as stated above, the novels are pretty explicit about the fact that the only person Shion is interested in is Nezumi.
- Spell My Name with an "S": Shion/Sion.
- Violently Protective Boyfriend: Do not insult or endanger Nezumi if you want to remain unharmed.
- Wide-Eyed Idealist: He's more on the cynical side, but firmly believes that a bright future is attainable. In the end, he's successfully helping to build that future.
- Yandere: Downplayed since he lacks the crazy part, but he can get violent when Nezumi is on the line, even for minor, non-threatening issues.
"That man tried to kill you, so he had to receive punishment."
- In the novels, Shion is close to strangling a man because he tried to kill Nezumi. Only when Nezumi pleads with him to stop does he snap out of it. And then there's his explanation as to why:
- He also violently attacks Rikiga for simply making a pass at Nezumi and later shoots a guard/Rashi at point-blank range after he seriously injures Nezumi..
A cynical young man with a dark past. He was saved by Shion when they were younger, only to return the favor years later. Due to his experiences in No. 6, he hates most everything about the city and its people, and is perfectly willing to watch it fall.
- Attractive Bent-Gender: As his local theater was swift to notice, Nezumi makes a really good-looking woman.
- Bishōnen: Pretty enough to be hit on multiple times and to play in drag as the beautiful Ophelia.
- Chastity Couple: His and Shion's relationship is not portrayed as overtly sexual, at least in the anime and manga. in the light novels, however...
- Cultured Badass: His room is cramped with bookshelves filled with classical literature, and he's an actor by trade.
- The Cynic: Especially compared to Shion, though he does have moments where this is inverted later in the anime/manga.
- Dark and Troubled Past
- Deadpan Snarker: Hoo boy, does he get called out on that one.
- Defrosting the Ice King: As Hosoya-san puts it, "He doesn't change so much as he loosens up. He always had those emotions but because of Shion he allows himself to feel them." note
- Dude Looks Like a Lady: He makes such a convincing woman that he's made a career out of it — he's a Shakespearean actor who specializes in performing as female characters.
- Easily Forgiven: Shion was furious when Nezumi admitted that he was using Safu as an excuse to break in the facility for his own agenda. All is forgiven when Nezumi is seriously injured (only a few minutes after the revelation) and Shion rushes to heal him.
- Even the Guys Want Him: Shion being the main example. There is also the two mooks who wanted "payment" from him after he kisses the prostitute, and is also implied by Rikiga when he offers Nezumi a job as a gigolo.
- Gray Eyes: Occasionally silver. Shion can hardly go without mentioning them.
- Homoerotic Subtext: Invoked deliberately with Shion. Later becomes plain text.
- It's All My Fault: Shion killing a guard/Rashi makes him break down and blame himself for corrupting him.
- Jerk with a Heart of Gold: He can be a jerkass at the very least. But he also sings to Inukashi's dying pack members to ease their suffering, to say nothing of what he'll do where Shion is concerned.
- Only Known by Their Nickname: For lack of a given name; he had one at a point, but he can no longer recall what it was.
- Last of His Kind: Nezumi is all that is left of the Forest People that lived on the site where No. 6 was built.
- Tall, Dark, and Snarky: He's got a good few inches on Shion with long dark hair, and a particularly mordant disposition.
- Magical Native American: An ostensibly Japanese version of one. He can "hear" nature, and can sing a song of calming.
- Meaningful Nickname: "Mouse" or "Rat", a name given to him after escaping the destruction of his homeland and the slaughter of his people. His real name is never revealed in-series.
- He also goes by "Eve" when onstage. Two guesses as to who Adam is...
- Official Couple: With Shion
- Real Men Wear Pink: He's as likely to shank you as he is to quote Romeo and Juliet at you in a dress and a full face of makeup, besides being a wonderful singer and dancer. It's all a part of his charm.
- Scars Are Forever: The massive burn scars on his back are courtesy of the flamethrower-wielding No. 6 soldiers that slaughtered his people.
- Taking the Bullet: For Shion when they're trying to escape the Correctional Facility and Shion doesn't notice the guard aiming at him because of his despair over Safu. It's almost enough to drive Shion to the breaking point in manga/novel though he ultimately survives.
- Tears of Remorse: When Shion shoots a guard/Rashi (depending on anime or manga/novel he breaks down, blaming himself.
- Tsundere: Especially towards Shion. He'll deliver an angry rant at No. 6, but the moment he sees Shion is upset he gently comforts him. Also, maybe towards Inukashi if you tilt your head and squint, though he'd probably die denying it.
- What Beautiful Eyes!: In the novel, Shion almost cannot mention Nezumi without talking about how beautiful his eyes are.
- Wholesome Crossdresser: As part of his acting job. He's very good at it, too.
- You Gotta Have Blue Hair: Blueish, grayish, off-purplish, depending on who you ask. It's clearly supposed to represent black, though.
Residents of No.6
Shion's childhood friend and a fellow resident of No. 6. Like Shion, she's a child genius - her expertise is the human brain and to a degree, psychology. Also like Shion, Safu begins to show doubt about the utopia that is No. 6.
- Ambiguous Disorder: Often seems lost in social situations, such as her proposal to Shion or cluelessness about romance when studying abroad. However, her behavior may just be a result of growing up as a sheltered child prodigy.
- Ascended to a Higher Plane of Existence: She becomes a physical medium for Elyurias.
- Adaptation Expansion: She is given a much larger focus in the Anime than in the original novels.
- Berserk Button: Go ahead, interrupt her presentation on the human mind or insult her grandmother.
- Brain in a Jar: Though it was never explicitly shown what happened to her body after the operation, we can be sure there was not much left of it (aside from her brain, perhaps...). As in the manga version Safu that Shion and Nezumi met in Correction Facility was merely a projection that "came to life", because Elyurias made her wish "I want to meet Shion one more time" come true.
- Brainy Brunette
- Child Prodigy
- Damsel in Distress: After being captured by the Bureau of Public Security. Turns into a Damsel out of Distress when she uses Elyurias' power to help Nezumi and Shion by controlling the Correction Facility's computers, although her role consists less of kicking ass and more of standing around and looking kinda creepy.
- Heroic Sacrifice: When Nezumi and Shion blow up Mother, she stays behind with Elyurias in order to destroy it for good.
- Incompatible Orientation: The fate of her affections toward Shion since Safu just happens to not be Nezumi.
- I Want My Beloved to Be Happy: Tells Shion she's fine with him having a girlfriend while she's gone and brings him Back from the Dead (in anime only) while possessed by Elyurias before Ascending to a Higher Plane of Existence
- No Social Skills: She functions well in No. 6, however she's seen as odd by her peers when she studies in No. 5. It certainly doesn't help that her way of asking Shion to have sex with her is "I want to have your sperm."
- Sweater Girl
- Unlucky Childhood Friend: Shion flat-out states in the novels that while he treasures her as a friend, he does not and cannot return her romantic feelings. Aside from Shion's attachment to Nezumi, circumstances just do not work in her favor.
- Walking Spoiler: Really, one can't really talk about her without spoiling the end of the series.
Shion's mother. With Shion, she was sent to live down in Lost Town where she opened up a bakery. She and Nezumi contact one another through strips of paper brought by mice.
- Dude Magnet: She has a lot of admirers...
- Friend to All Children: Thinks children are adorable, and strongly believes it is an adult's responsibility to protect them.
- Good Parent: She really loves Shion and isn't upset at all about their downgrade from a life of luxury.
- Mysterious Past: At least one photo of her exists with the Founding Members of No.6. She also knew where Rikiga was likely to be in the West Block.
One of the residents of No. 6, and a resistance fighter. Yoming first begins to suspect something is amiss in the city when his wife and child mysteriously disappear. He takes interest in Karan after Shion's disappearance.
- Conspiracy Theorist: Luckily (or unluckily), the conspiracy is real.
- Karmic Death: Though starting out with the intention of avenging his family's death, he eventually descends into creepy and unwanted advances on Karan and gleefully planning to incite a mob bloodbath on No. 6's founding anniversary. He ends as another victim of the birth of the wasp.
Residents of the West Block
One of the residents of the West Block outside of No. 6. Inukashi, quite literally "Dog Keeper," is a brash, often dangerous individual who spends their time either renting out their many dogs as heaters during the winter or smuggling in items to sell from an illicit contact within No. 6's correctional facility. They have a very violent, volatile relationship with Nezumi, but Nezumi still often goes to them to gather information - for a price.
- Ambiguous Gender: Assumed by some to be female, based on their small stature, nice legs, and one mention of 'softness' when they were hugged, however official information does not give a definite answer one way or another.
- Samus Is a Girl: Treated by the other characters as male, until used as bait to lure in a No. 6 higher-up: Shion, trying to comfort Inukashi afterward, wonders if his friend might actually be a girl. The rescued baby from episode 10 also calls Inukashi "mama". Even so, Inukashi never personally discusses their gender identity, so there's no way to know.
- Crossdressing Voices: Sort of.
- Berserk Button: Inukashi does not react well when their dogs, especially their "mother", are insulted.
- Japanese Pronouns: Refers to themselves with the aggressive-masculine ore.
- Meaningful Name / Only Known by Their Nickname: Inukashi literally means "dog-keeper", or "dog-loaner".
- Raised By Dogs: Their "mother" was a dog that offered milk and kept them safe.
- Tsundere: Only towards Shion. Maybe, maybe towards Nezumi too. Shion thinks so, Inukashi — like Nezumi — would die before admitting it.
One of the residents of West Block. He runs a prostitution service which allows him a life of luxury in comparison to other residents. At one point, he wrote articles regarding No. 6.
- Cowardly Lion: He really doesn't want to get involved in Shion and Nezumi's plans, but does so anyway.
- Fanboy: He really likes Eve, Nezumi's stage persona. He's less charitable towards Nezumi, given that well, it's Nezumi.
- Intrepid Reporter: Hinted that the reason he was sent to live in West Block was due to his articles questioning No. 6's activities.
- Parental Substitute: He tries to be this to Shion from time to time, given that he's still attached to Karan.
A mysterious entity, subject to much research by the scientists of No. 6. Elyurias once existed in the forest that was destroyed by No.6's operatives, and has power over nature. She was worshiped by the Forest People as a god. No. 6's government has gone to great lengths to research how to control her power.
- Bee Afraid: Elyurias occasionally appears as a giant one.
- Gaia's Vengeance: Unleashes this on the city during the ending.
- Face Full of Alien Wing-Wong: Elyurias reproduces by laying eggs in the bodies of other species. Namely, humans. The process of a bee being born causes the host to rot away very, very quickly.
- Symbiotic Possession: Though forcibly implanted into Safu, they do not seem to bear each other ill will.