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- Voiced by: Hiro Shimono (Japanese), Sean Michael Teague (English)
- Cheerful Child: Though his age is unknown. He could be anywhere from 10 to 15, really.
- Children Are Innocent: He knows next to nothing about the world except what Karoku taught him, unknowing of what "blood" is and what it means when it's splattered outside the body.
- Constantly Curious: He's always running off and getting lost in crowds because of this.
- Everything's Better with Rainbows: It's what his species name, Niji, means. He originally lived in the Niji Forest, and he later somehow casts a large rainbow in order to find Karoku.
- Good Is Dumb: Justified, considering that he was originally a cute little animal, and looks like and is later referred to being a child as well. However, unlike some character types who remain clueless throughout the story, he's slowly learning more about the world.
- Heroic Albino
- Humanity Ensues: Originally a cute animal called a Niji, he was somehow transformed into a human in an as of yet unspecified way.
- Innocent Inaccurate: He described blood as "red water."
- Morality Pet: Seems to be one for just about everyone in Circus to a varying degree, but none more so than with Gareki.
- Nice Guy: Very kindhearted and gentle.
- Red Eyes, Take Warning: Subverted, he is incredibly naive and would barely hurt a fly... unless an animal was about to kill Karoku.
- Ridiculously Cute Critter: In Niji form.
- Super Senses: Despite his not having any offensive abilities at the moment, Nai is far from being The Load, as his elevated hearing has more than once been crucial in ensuring the survival of those around him, and later, useful during missions.
- Tender Tears: Several times, most notably in episode 3.
- Zettai Ryouiki: A male example, Grade A.
- Badass Normal: He doesn't have any special powers like the rest of the cast. His weapons of choice tend to be guns and explosives he makes himself.
- Big Brother Instinct: He develops this behavior for Nai. At one point, he encouraged Nai to run off without him so that he wouldn't be attacked by a Varuga. He also developed this to his foster siblings, Yotaka and Tsubame.
- Bring My Red Jacket
- Celibate Hero: In chapter 12, Yogi mentions how cool Gareki can be when Gareki easily shoots down a bracelet in a booth that Yogi had been trying to get, and how he probably has several girlfriends. However, we see no evidence that Gareki's interested in girls, or romance in general.
- Combat Medic: Currently in training to be such.
- Dark and Troubled Past: He was sold by his parents to a human trafficking group. While being transported, the ship he was on crashed. He was later picked up by Tsubaki who took care of him along with her younger siblings. She was later killed by Yotaka who was transforming into a Varuga due to the medicine that she received from her "boyfriend". What makes her death more tragic is the fact that Gareki warned Tsubaki not accept the medicine and she didn't listen to him, not out of malice, but out of love for her siblings.
- Defrosting Ice King: Nai (unwittingly) and Yogi (determined) together with other Circus members have gotten him to open up considerably.
- Gadgeteer Genius: Made particularly apparent through his contribution to the mission to save Karoku in volume 7.
- Goggles Do Nothing: Averted. He's wearing them in his first appearance, having just blown up a portion of the mansion where he meets Nai. They don't get much use after that, though this is justified by the fact that he has no need for explosives after being taken aboard Circus's second ship.
- The Gunslinger: What he might be, if Circus allowed him to use his gun.
- Handguns: Gareki likes using them. Circus doesn't like his use of them.
- Healthcare Motivation: He originally got into thieving to pay for his foster grandfather's medical bills.
- Jade-Colored Glasses: The losses in his childhood, which includes being sold as a slave by his parents and seeing his Parental Substitute being exploited, as well as life on the street have made him very cynical about people (himself included) and unwilling to make friends.
- The Smart Guy: Despite the implication of his street savvy, Gareki's shown and later noted to read frequently during his time in Circus, which heightens the poignancy when what he was reading up on is revealed in a conversation with Hirato in chapter 38. His skills as an unsung Gadgeteer Genius backs this position up further.
- Street Urchin: Gritty type. Prominent early on, though the circumstances over why are explained later. He does mellow down once he and Nai wind up with Circus, becoming broodier and using less dirty tricks. His sharp intellect's evident throughout, however.
- Stuff Blowing Up: Is very knowledgeable about explosives. He was even introduced setting up a bomb.
- Tsundere: Gareki can be a platonic Type A, especially when Yogi teases him. Also to Nai, though less violently. He's normally aggressive verbally and physically, but when he's around friends or family, he shows his dere side.
- Aloof Big Brother: For the most part, but it's subverted in chapter 52, where he breaks down in tears when Nai is close to death.
- Bandage Hunk: He's always in bandages in-story for undisclosed reasons.
- Dark and Troubled Past: As the Circus bracelet left behind in blood indicates.
- Evil Twin: It's very possible that the Karoku who is working for Kafka is this to the one who took care of Nai.
- Kidnapped Scientist: If he really was involved in the creation of Nai, who's successfully existing as a new hybrid species, then it is very likely that he was abducted for his knowledge of genetics as well as his ability to create a stable life form, an aspect in which Kafka's valga have fallen short.
- Manipulative Bastard: He seems to manipulate events around him for his benefit. This is an implication that this Karoku isn't the same person that Nai was with before.
- Nice Guy: Nai thinks of him as "as warm as the sun". Later events hint that there's something sinister about him, but only when "the other Karoku" is in control.
- Not So Stoic: In chapter 52, after regaining his memories of Nai, he loses his usually composed disposition and breaks down in tears when Nai is close to dying from his injuries.
- Psychic Link: He seems to be able to communicate with Nai this way under certain circumstances.
- Teen Genius: Heavily implied to have had a hand in the creation of Nai as a Niji-human hybrid.
- Trauma-Induced Amnesia: After he's rescued from Kafka by Circus, his memories become so scrambled that he entirely forgets his relationship with Nai. Dr. Akari suggests it's because of the stress of his previous circumstances.
- You Gotta Have Blue Hair: Exactly What It Says on the Tin
- Your Days Are Numbered: Implied. A servant of the Kafka manor where he is staying comments that it's a waste to feed him.
- You Have Outlived Your Usefulness: Implied when he suddenly tells Nai through their telepathic communications that he's going to be killed soon if Nai doesn't come rescue him.
Circus Second Ship
- Cane Fu: Hirato's weapon of choice, with the special attack "Vakuum."
- The Captain
- Father to His Men: His affection for his crew is more concealed than most examples of this trope, and may manifest in strange ways (due to his love of provoking others), but he does things like buying candy and souvenirs for Nai and arranging for Gareki to attend school in the hopes of getting his license to officially join Circus. These tendencies are perhaps best viewed in his interactions with Tsukumo, though YMMV on whether you read it in a romantic context or not.
- Foil: To Akari. Hirato is a seemingly friendly Bitch in Sheep's Clothing whose job is to eliminate lives, while Akari is a serious Jerk with a Heart of Gold whose job is to save lives.
- Manipulative Bastard: And always seems to have a plan and is one step ahead of everyone else.
- Noble Demon: Says to Akari rather wistfully that it's his job to take lives but as seen in flashbacks with his first encounter with Yogi, Hirato is not quite as ruthless as he'd like everyone (and himself) to believe. Not to mention how protective he is of his "children".
- Papa Wolf: He may be the Stoic Glasses and furthermore, a Manipulative Bastard, but Hirato does NOT like it when people mess with his "children."
- Parental Substitute: His increasingly coming off like one or some kind of familial figure to Gareki (and Nai), despite being a bit aloof, is lampshaded a few times later on in the series, including by allies on the Third Ship.
- Passive-Aggressive Kombat: Master of this, as part of his Manipulative Bastard package. Played for Laughs when he's around Akari.
- Scary Shiny Glasses: On occasion.
- The Southpaw: Wields his cane with his left hand.
- Stoic Spectacles: Hirato fits this to a T.
- Tranquil Fury:
- Though almost impossible to read most the time, he has a moment of this as early as chapter 14 when, after Yotaka fought against and injured Yogi, he pursued the person responsible and just after talking with him calmly, says, "It is enjoyable to torment, isn't it?", (even sporting a pleasant smile to boot) before having his banshees tear him apart.
- Another time this happens is in chapter 35 when Azana betrays and tries to kill Akari. He doesn't smile this time or have any sarcastic remarks, but he knocks Azana away and calmly states the punishment for attacking someone of SSS rank before attacking. If Akari hadn't stopped him, he would have killed Azana without a second thought or any emotion on his face at all despite his anger. Do not dare to hurt Akari.
- Voiced by: Mamoru Miyano (Japanese), Christopher Bevins (English)"The soaring male spirit, the heart-throbbing sparkly prince, National Defense Organization 'Circus' Second Ship member Yogi!"
- Adorably Precocious Child : His greatest concern as a child was not being able to become as good a king as his father so he spent a lot of his youth studying politics and body-guarding his sister.
- Afraid of Doctors: Specifically of Doctor Akari, to the point of amusement for the audience. Becomes less amusing once the details of his childhood as an experimental subject in various medical and biotechnological research labs are revealed, though admittedly he doesn't remember them. But his memories of being experimented on in Akari's lab weren't lost, so the phobia is pretty self-explanatory once his backstory is revealed.
- After-Action Healing Drama: He tends to get badly injured more often than the other main characters, requiring treatment from Akari or even hospital stays. Of special note are the Rinoll and Merumerai arcs.
- Alternate Identity Amnesia: Golden!Yogi and Silver!Yogi don't seem to clearly share memories between each other, though the silver persona is more aware of what the normal one is doing than vice-versa.
- Beware the Nice Ones: Can become pretty badass when the need calls for it, despite his default Nice Guy persona.
- Big Brother Mentor: To Gareki (mainly about enjoying life and bonding with other people) and Nai.
- Broken Tears:
- In chapter 18, after the allergy patch that holds back his split personality falls off, tears start streaming down his face for no reason other than this. Given his usually sunny disposition, it's quite disconcerting.
- Happens again in chapter 102 when his memories return.
- Butt-Monkey: Gets a lot of abuse from pretty much everyone except Nai; most notably Gareki (of the physical sort), Hirato (of the verbal sort) and Eva. Kiichi, Akari, and the Second Ship's doctor pitch in from time-to-time as well.
- Crouching Moron, Hidden Badass: Usually acts like a ditz, but is capable of both intelligence and badassery when things get serious.
- Cuddle Bug: He enjoys giving hugs to his teammates.
- Dark and Troubled Past: The cause of both his Split Personality and Trauma-Induced Amnesia. It was a good life at first, and then everything went to hell.
- The Ditz: His default persona.
- Dual Wielding: Two épées made of strong, thorny vines.
- Escaped from the Lab: As his backstory reveals; though he was technically rescued from it, he'd killed all the workers there by the time he was found by Circus... and taken right back to their lab. Poor kid.
- Forced to Watch: As a ten-year-old, was strapped to his surgery table and forced to watch a video where his little sister was literary torn to shreds, all while pleading for his help.
- Friend to All Children: His role in the acts that Circus puts up, but he's genuinely fond of kids and the kids love him, too.
- Green Thumb: Yogi's weapons are two thorn-like épées, and he can conjure up thorny vines with them as well. Combined with Scarf of Asskicking in chapter 19, whereupon the badass split personality of Yogi saves Gareki from the split personality's own attack this way.
- Harmful to Minors: Being forced to watch his nearest and dearest being brutally killed at the age of ten.
- Hair of Gold, Heart of Gold: Unarguably one of the two nicest characters in the story: always willing to help out when he can, loves children, and is very apologetic and genuinely saddened when they have to kill someone.
- Heroic B.S.O.D.: Finding the decapitated corpses of his caretakers as a child. Relives it again when his memories return.
- Hidden Depths: Yogi can be melodramatic and flamboyant one moment, then more serious than Kiichi the next. There's definitely a lot of this going on, and it's slowly revealed over the course of the series.
- Keet: Except during serious fights/situations, he's always bright, loud, cheerful and sports a childish streak a mile wide. However, later events in the manga hint that this is likely due to the ten-year gap in his memories.
- Knight in Shining Armor: His "role" in Circus shows, hilariously combined with a mascot costume.
- Nice Guy: See the Hair of Gold, Heart of Gold entry, above.
- The Patient Has Left the Building: When he ran away to Vinto.
- Pointless Band-Aid: Averted. It's actually a medicinal patch that administers allergy medicine. And, strangely, keeps his split personality in check.
- Stepford Smiler: Somewhat. Silver!Yogi in particular is this to a tee.
- Sole Survivor: Of the tragedy in his home country. Later subverted when we learn that his younger sister also survived.
- Something About a Rose: The kanji for one of his defense techniques is "Rose Barrier."
- Split Personality: His usually gold hair turns silver as an indication.
- Sunny Sunflower Disposition: Which makes it all the more shocking how his behaviour changes when his other personality manifests itself and, later, when his memories start to resurface.
- Trauma-Induced Amnesia: He doesn't remember the first 10 years of his life because of the terrible experiences he went through as a child. His other self seems to have retained some memories, but disregards them as nightmares.
- "Numerous stars fall from the sky. The little lamb knows the sky. National Defense Organization Circus Second Ship member Tsukumo."
- Action Girl
- Big Sister Mentor: To Gareki and Nai.
- Dies Wide Open: At the end of episode 9, courtesy of Karoku. However, by the start of episode 10, she was later brought back to life by Hirato.
- Disguised in Drag: Does this with Kiichi while undercover on a later mission.
- Distress Ball: She's usually competent, but when the plot calls for someone to be rescued, well, it's either her or Nai.
- Even the Girls Want Her: In-universe, Eva.
- Heroic Self-Deprecation: She constantly questions if she has fulfilled her duties, and frets when something's less than perfect.
- Lady of War: As her specialty is in acrobatics.
- Light 'em Up: Her powers and attacks involve stars and constellations.
- Parental Neglect: While her parents where originally just stern or discriminative, her situation developed into this when her older, more loved, brother died trying to save her.
- Rapunzel Hair
- The Stoic
- Not So Stoic: When her teammates are in danger.
- Sugar and Ice Personality: Normally quiet and emotionless, but sweet and protective towards her teammates.
- Undying Loyalty: To Hirato.
- Waif-Fu: Tsukumo is extremely strong despite how petite and slender she is.
- You Should Have Died Instead: In her parents' oppinion
- Zettai Ryouiki
- Voiced by: Yoko Honna (Japanese), Jessica Cavanagh (English)"I command the stones. Bury the demon in dazzling brilliance. I am enthroned as the Queen of the Sapphire Crown. National Defense Organization "Circus" Second Ship member Eva."
- Action Girl
- Bare Your Midriff: Occasionally.
- Boobs of Steel
- Cool Big Sis
- Does Not Like Men: Played for Laughs
- Kicking Ass in All Her Finery: That long flowing dress does not hinder her in the least.
- Lady of War
- Lipstick Lesbian: She dresses in feminine clothing and is strongly implied to have feelings for Tsukumo.
- Ms. Fanservice: She tends to wear revealing clothing.
- Power Crystal: Her weapons of choice.
- You Gotta Have Blue Hair: Green hair.
Circus First Ship
- The Alcoholic: Played for Laughs
- The Captain
- Foil: The noisy, cheerful and seemingly silly Captain to Hirato's calculated and suave manners. He's by no means incapable though.
- The Fool
- Friendly Address Privileges: Loves to call Akari-sensei "Akari-chan", a fact that irritates the doctor as he is older than him. According to the short extra after chapter 72, he even called him that when Akari used to be his instructor in Kuronomei.
- Not a Morning Person
- Hidden Depths: While he comes off as much more laid-back than Hirato and Akari, his expression turns quite sinister at one point when he asks Tsubame what she's willing to sacrifice to protect the people around her.
- Large Ham
- Action Girl
- Bratty Half-Pint: She's the shortest person on Airship One and tends to talk down to other people, especially those who are older than her.
- Disguised in Drag: Does this with Tsukumo while undercover on a later mission.
- Elegant Gothic Lolita
- Little Miss Badass
- Older Than They Look: She definitely doesn't look fifteen.
- Pet the Dog: Despite her usual tsun to everyone, she was the only one who comforted Nai when the amnesiac Karoku wasn't at his best with him. It's hinted a bit later that she really does care for him.
- The Rival: To Yogi in particular because she resents having the same grades as him, whom she thought useless because of his unwillingness to harm others.
- Sinister Scythe
- Third-Person Person: There are times where she slips into this while she talks in first person other times.
- Tsundere: A fierce type A to anyone she considers slacking off or not trying hard enough. She does have her rare dere moments though.
- Unknown Rival: To Tsukumo.
- You Gotta Have Blue Hair: Exactly What It Says on the Tin
- Big Creepy-Crawlies: What his more powerful attacks involve.
- Bitch in Sheep's Clothing: Zig-zagged. Underneath his politeness, he is actually aloof and capable of nasty words and actions, as Gareki learns firsthand. On the other hand, he's dedicated to his comrades, as a true Circus member will.
- Dye Hard: His hair is actually gray, but he constantly dyes it.
- Jerk with a Heart of Gold: When he's not being a Bitch in Sheep's Clothing.
- Mad Scientist: He loves experimenting with medicinal herbs and dangerous plants.
- Older Than They Look: He's 27, apparently.
- Ship Tease: It's implied that he may have a crush on Tsukumo.
- Stoic Spectacles
- Whip It Good
- Always Someone Better: To Azana.
- Brutal Honesty/Deadpan Snarker: "What's wrong with telling the truth? If you don't like it, then improve things!" That line says it all. Another example◊
- Bunnies for Cuteness: The flower bunny that he takes care off is meant to represent his soft side. In the fanbook it is stated that it brings him joy to take care of it. I mean the bunny refuses to return to the wild to stay with him. You cannot get any cuter than that.
- The Charmer
- Cross-Popping Veins: When he is angry but not yelling Here
- Color Contrast: Black/White contrast with Hirato as another way to remark their foil status.
- Curtains Match The Windows: Light pink hair and light pink eyes.
- Dressed to Heal
- Dr. Jerk: In Yogi's opinion, but not really true.
- Foil: To Hirato. Akari is a serious Jerk with a Heart of Gold whose job is to save lives, while Hirato is a seemingly friendly Bitch in Sheep's Clothing whose job entails taking lives.
- Friend to Bugs: In the Drama CD of a character song it was revealed that he likes insects and would not allow Hirato and Tsukitachi to harm one when it escaped and ruined his lab.
- Freudian Trio: The Super Ego, Hirato is the Ego and Tsukitashi the Id.
- Food Slap: In the Drama CD's when Hirato and Tsukitachi upset him too much, he threw wine to both of their faces.
- Good Is Not Nice: Although he is a very kindhearted person and means no harm, he is rather harsh and domineering.
- Hospital Hottie: It's Lampshaded with the nurses, who both fawn over him and hilariously deny him whenever he tries to use his charms to make them do things.
- Jerk with a Heart of Gold ◊
- Parental Substitute for Azana.
- Labcoat of Science and Medicine: In this case is both since he is both a doctor and a resercher. Almost never seen without it.
- Messy Hair: He actually looks younger and nicer with it. 
- Mr. Exposition: Most of his conversations involve him explaining something to someone else.
- Names to Trust Immediately: Part of the Vinto arc was about how the drugs were distributed because someone was using his name. 
- No Sense of Humor: Once again lampshaded by Tokikatsu in a omake. Here◊
- Not So Stoic: When he discovers that Azana was poaching in vinto and then when he tells him that he hates him. It is far more dramatic in the CD drama, but the face he makes in the anime was really sad. ◊
- Omnidisciplinary Scientist/Super Doc: Not only does he have medical knowledge, he also has knowledge and does research concerning biology, archeology, genetics and pharmacology as he is the Research Tower´s Research Chief Specialist. Relating to his medical knowledge he is also a surgeon, an expert in emergency medicine, fixing fractures, making his own medicine (Yogi's allergy patch). That indeed takes a lot of different medical specialties. No wonder he is a SSS rank.
- Perpetual Frowner: You almost never see him smile unless he's smirking.
- Proud Elite
- Sitcom Archnemesis: Mainly to Hirato.
- Spock Speak/Techno Babble: He always talks in very scientific terms, most notably in the manga, especially when making explanations.
- The Stoic: ◊
- Twitchy Eye: ◊ ◊
- Vitriolic Best Buds: Although he acts antagonistic towards Hirato and Tsukitachi he ends up spending his free time with them drinking (initially not willingly of course). Both Hirato and Tsukitachi both care for him as well and make sure he takes a break once in a while. They were both worried for him after the incident with Azana.
- You Gotta Have Blue Hair: Pink in his case.
- Workaholic: He does not believe in taking breaks or rest. It is lampshaded by Tokikatsu in a message he sent him. ◊ ◊ ◊
- A Pupil of Mine Until He Turned to Evil: To Akari.
- Beware the Nice Ones
- Broken Bird
- Broken Tears: 
- Driven by Envy: Tried to kill Akari.
- Freudian Excuse: His entire family was killed by Valga.
- Irrational Hatred: He hates Akari because he considers him a perfect being, even if Akari has been nothing but nice to him since he took care of him after his family were killed by Valga.
- The Klutz
- The Resenter: Towards Akari. ◊
- Social Darwinist
- Secret Test: By Hirato when left alone with Akari to see whether he would remain loyal or he would desert.
- Traitor Shot: Suspicious...◊
- Clingy Jealous Girl: Towards Karoku.
- Curtains Match the Window: Pink hair and pink eyes.
- Girlish Pigtails
- Loving a Shadow: It's obvious that she isn't aware of Karoku's personality at all.
- Spell My Name with an "S": Her official Japanese name in the guide book is Erishuka, but the English translation makes it as Eleska.
- Spoiled Brat
- The Ojou
- Voiced by: Junichi Suwabe (Japanese), Brandon Potter (English)
- Badass in a Nice Suit: His default attire.
- The Dragon: He appears to be this to Palnedo, even taking the fall for him after the whole Smoky Mansion fiasco.
- Bare Your Midriff: Despite being in the snow.
- Monster Clown: At least appearance wise.
- Those Two Bad Guys: With Kagiri.
- Voiced by: Toshiyuki Toyonaga (Japanese), Tyson Rinehart (English)
- Big Brother Instinct: Big time for Tsubame. After their older sister died, he took it upon himself to take care of his twin.
- Childhood Friends: To Gareki.
- Half-Identical Twins: In his youth, he looked just like his twin sister except with purple hair and eyes. He has his hair cut in his teen years
- Jerk with a Heart of Gold: He initially seems aggressive, but he cares about his sister and Gareki.
- Killed Off for Real
- Suicide by Cop: When he's forced to strangle his sister, he begs Gareki to kill him.
- Tragic Monster: He was turning to a Varuga because he had consumed some of the "medicine" that Tsubaki's boyfriend gave her. He makes it clear in his final moments that he acknowledged that he's killed and possibly consumed people in the past and is mortified by his actions.
- Twin Telepathy
- The Atoner: Sort of. After losing her brother in a very nasty way and knowing that he was sacrificing himself for her, she becomes determined to help in stopping Kafka
- Break the Cutie: Everything to do with her brother's death.
- Childhood Friends: To Gareki.
- Nice Girl
- Take a Level in Badass
- Twin Telepathy
- Cool Big Sis: To Gareki, Yotaka, and Tsubame.
- Death by Origin Story: Her death had a huge impact on Gareki's personality and outlook in life.
- Deceased Parents Are the Best: Took in and treated Gareki as her own.
- Nice Girl: She took Gareki out of nothing, but pure compassion for him. She also did everything she could to take care of her family. Unfortunately, her kindness was taken advantage by a Varuga who gave her pills, which transformed her younger brother into a murderous creature.
- Parental Substitute: She became one for Gareki whose parents sold him at a young age and was Promoted To Parent for her younger siblings.
- Rapunzel Hair
- Voiced by: Mutsumi Tamura (Japanese), Lara Woodhull (English)
- All of the Other Reindeer: Was bullied by the other servants of the mansion she worked for
- An Arm and a Leg: Quite literally
- Back from the Dead
- The Determinator: Suffered through life threatening injuries, insomnia, abuse, neglect and sexual harassment, was near suicidal but still refused to back down.
- Green Thumb: Can make flowers bloom from thin air. She also works as a gardener.
- Last of His Kind: Aside from Yogi, she is the only known survivor of the Rimhakka tragedy. The people of her home country harbored a special genetic build-up that granted them cradle powers (without the use of bracelets)
- Long Lost Sibling: To Yogi
- Trauma-Induced Amnesia: Just like her older brother.
- Walking Spoiler