The main character of the story, a girl who is the only person in the world who does not have a Servant.
- Conveniently an Orphan: Her parents died when she was really young, setting up her distaste for her grandmother's presence and her attachment to Caren as her parent figure.
- Cursed with Awesome: While it's downplayed, due to her not possessing a lot of the abilities of other humans, such as immortality, Erice was born with Evil Spirits residing in her that she can synchronize with to acquire demonic abilities. She uses this power to act as a City enforcer against criminal Servants and Masters.
- The Dreaded: In spite of, or because of the above and below mentioned tropes, Erice is actually a trained Servant Killer tasked with taking down uncontrolled Servants. She is fourteen years old, just for reference.
- Experienced Protagonist: She already has a reputation as the Servant-killing "Grim Reaper" from the very start.
- Expy Of Kiritsugu Emiya from Fate/Zero. Both are The Dreaded in their respective series, with Kiritsugu being rightfully feared by magus since he doesn't play by traditional rules and Erice being specifically trained to kill Servants.
- Normal Fish in a Tiny Pond: Inverted. She is literally the only person in the entire world who isn't special in the same way as everyone else. She isn't immortal, can't control her physical age with Command Seals, and until she contracted with Voyager, she didn't have a Servant. She wasn't born with a Holy Grail either.
- Un-Sorcerer: Subverted. The promotional material plays out the fact that she is the only person without a Holy Grail inside them. In reality, she is far from being just a regular human, as an experienced Magus with a collective of evil spirits inside her.
Friend of Erice and the Master of Berserker.
- Muggle Best Friend: Well, a Muggle under the operative rules of Requiem's status quo, she's primarily used to illustrate how odd Erice's status is in contrast to everyone else.
Master of Saber. Also known as Haruko, she represents the Riedenflaus family who are funding Akihabara's Holy Grail tournaments.
- Arbitrary Skepticism: Despite all the feats achieved by humans with verifiable evidence to back it up with the existence of Servants and other means, she believes it to be highly unlikely that humanity even had the technology in 1969 to reach space, let alone send someone to the moon.
- Fusion Dance: She can use Heroic Spirit Possession to fuse with Galahad Alter.
Erice's grandmother and the Master of Lancer. She won a Holy Grail War at some point in the past.
- The Jinx: Chitose is seen as one by Erice because of all the misfortune she brings whenever around Erice, like the death of Erice's parents.
- Older Than She Looks: As a prime example of how humanity has stopped aging and modifies their bodies as they see fit, she is Erice's grandmother yet looks like a young adult.
A series of four AIs who monitor the Mosaic City. The most important of the four is Caren Fujimura who is Erice's home teacher, mentor and the one who gives her missions.
- Anime Chinese Girl: The Caren AI who monitors Shinjuku wears a qipao and hair buns.
- Mythology Gag:
- All the Carens seen so far have surnames related to characters in Fate/stay night. Caren Fujimura shares hers with Taiga while Himuro, Saegusa, and Makidera are taken from Homurahara's track team trio.
- Caren Fujimura is also a reference to when her baby version was legally adopted under Taiga's name in Capsule Servant.
- Parental Substitute: Erice regards Fujimura as her guardian and caretaker much more than her grandmother.
- The Anti-Nihilist: He is surprisingly joyful for a man cursed by God, believing that people should enjoy their lives in order to make them awesome.
- Pungeon Master: He is considered very irritating due to making constant undead puns and jokes.
- Really 700 Years Old: Comes with being an undead.
- Wandering Jew: The Wandering Jew who has lived as an undead up to the present and become a Master in the story. Fittingly, his Servant is another cursed wanderer, the Flying Dutchman.
The final Servant summoned to this world who Erice meets. He was referred to as simply 'Boy', before later being given the name Prin.
- Amnesiac Hero: He has no idea what his True Name is, what his class is and generally lacks basic knowledge of things.
- Bare-Handed Blade Block: He was able to catch Nzambi's knife with his finger, effortlessly hold it in place, then destroy it.
- Dramatic Wind: Even when indoors, his scarf ignores the lack of wind to flutter about freely. Erice chalks it up to his nature as a Servant.
- Only Known by Their Nickname: Due to not knowing his name, Karin gives him the nickname "Prin", due to Erice initially thinking him to be the titular Little Prince. "Voyager" is also a nickname given to him after his contract with Erice is finalized, not his class.
- Red Herring: His design evokes a lot of similarities with the Little Prince and even holds a toy plane resembling Saint-Exupéry's C.635 Simoun in the first volume's cover. However, when Erice tries to guess his True Name, he has no reaction to either the Little Prince or Saint-Exupéry, both Karin and Caren deny the possibility of him being either of the two, and the toy plane actually belongs to Erice.
- Why Did It Have to Be Snakes?: Although they don't show up, he is apparently deathly scared of snakes and is the one thing he will not approach. No matter how strong an enemy is, if it isn't a snake then he isn't afraid.
The Servant of Karin. Her True Name is Kijyou Koyo, better known as Momiji, a youkai which lived in the mountains of Nagano prefecture.
- Everything's Better with Dinosaurs: For some reason, she looks like a T-rex of some sort.
- Face of a Thug: She's a dinosaur oni yet most of the time she behaves like a large dog. Erice speculates this is why Karin rarely has her out in spiritual form at home because her parents already dislike the mere concept of the omnipresent Grails and Koyo would only serve as a reminder of them.
- Youkai: She is Momiji, an oni from Japanese folklore.
The Servant of Koharu. His True Name is Galahad, the son of Lancelot and one of the Knights of the Round Table, who has abandoned the holy knight's creed as an Alter Servant.
- Alternate Self: Of the original Galahad, who features elsewhere in the Fate series. As an Alter Servant, he's a darker version of the original.
- Cool Sword: One of his two swords is in fact the Sword of David
- Expy: His personality and relationship with his Master is similar to Archer's.
- Gender Flip: Subverted, as Erice initially mistakes Galahad fused together with Koharu as his actual identity.
- Handsome Lech: This version of Galahad takes after his father when it comes to women.
Servant of Chitose who won a Holy Grail War alongside her in the past. His True Name is Lucius Longinus, the Roman soldier who pierced Jesus' skin at the cross and the wielder of the Holy Spear.
- Reasonable Authority Figure: He is one of Erice's mentors, and is very compassionate to her.
- Blade on a Stick: She can reproduce a counterfeit of the Holy Spear Longinus itself.
- Griping About Gremlins: She can summon gremlins in large numbers.
- Resurrective Immortality: She is described as being cursed with immortality, but in a way that she would wander between worlds by resurrecting while keeping her memories until she would find her one true love.
- Cool Ship: The Flying Dutchman, which he can summon in his Noble Phantasm. It is an enormous galleon that's equipped with three dark masts from which crimson sails are flown, and its quarterdeck is described as intimidating and fortress-like over a pitch-black hull.
- Flying Dutchman: Has the Flying Dutchman as his Noble Phantasm, a ship full of the spirits of his old crew that are forced to wonder the seas with him and cut down invaders. It also has a conceptual curse that prevents him from docking at land except once every seven years. However, by that same curse, when he does make land he can dock anywhere in the world, even places with the greatest defences and magical barriers.
A Servant of unknown Class who begins killing people and raising them as zombies.
- Arc Villain: The main antagonist of volume one, having used her powers to disrupt the Holy Grail Tournament and cause a zombie outbreak.
- Necromancer: Nzambi is able to raise the dead as zombies with Voodoo due to her name being related to the origin of the word "zombie". This is even able to affect Servants, as shown with Hannibal.
- Oddly Shaped Sword: The sword she carries is abstract to say the least, but it is a case of Shown Their Work as well since there actually exists a sword in real-life very similar to it.