Koizumi

Biodata

Feature	Information
Name	Koizumi (古泉)
Gender	Male
Affiliation	Temporarily cooperates with Night Raid; aligned with the simulated Chaldea mission to resolve Singularities 8 35 40
Occupation/Role	Master; contractor and summoner of Servants; Singularity resolver
Status	Alive
First Appearance	Chapter 1

Power Progression

Stage / Realm / Level	Chapter	Notes
Remilia’s power manifests	5	Recognizes an internal power as Remilia Scarlet’s, attributed to their contract.
Temporary Vampire transformation	19	Remilia lends him her power; he becomes a vampire briefly and defeats Ouka’s group, but his perception of humans becomes distorted.
Initial Gungnir use and Vampire training	20 21	Materializes a pink spear and begins training against Danger Beasts and Hata no Kokoro; Noble Phantasm use causes severe exhaustion and risks berserk loss of control.
Improved control of Remilia’s power	28 29	Regenerates injuries and learns to better track Esdeath’s movements during repeated sparring, though he remains decisively outmatched.
Gungnir reaches Noble Phantasm-class output	32	His Gungnir pierces Hata no Kokoro’s attack and injures her despite her victory; Reimu recognizes his rapid growth.
Root Vortex connection / Yukari’s power	35	Survives an Assassin’s poison, connects to the Root Vortex, and touches the edge of Yakumo Yukari’s boundary-and-gap power without understanding how to wield it.
Assassin training and Serenity contract	38 39 41	Trains against Hundred Personas Hassan and Serenity Hassan; forms a contract with Serenity, whose Spirit Origin subsequently ascends.
Vampire power strengthened by first kill	44	Killing Reias’s lackeys and tasting human blood increases the Vampire power he can release, while intensifying his bloodlust and arrogance.

Background / History

Koizumi awakens in a ruined, unfamiliar city with no memory beyond eventually recalling his name. He is mortally wounded by a purple-haired Servant before Remilia Scarlet saves him, identifies herself as the Servant he summoned, and defeats the attacker with Gungnir. With no clear alternative and an unexplained sense of familiarity toward Remilia, he remains at her side despite her demanding treatment. 1 2

Yakumo Yukari later explains that he must resolve Singularities in parallel worlds by recovering or destroying Holy Grails that have set those worlds off course. She cannot explain his past, and her resistance to Command Seals prevents him from forcing answers from her. 8

Koizumi’s ability to summon Gensokyo-linked Servants is considered unusual. Gensokyo is absent from the Throne of Heroes, and a summoner ordinarily needs either a related relic or a personal connection to summon its residents; Koizumi used no relic. 18

During the Imperial Capital Singularity, he repeatedly suffers gaps in memory. He forgets time spent with Aerya, Sayo, Ieyasu, and Kurome, yet retains emotional familiarity with them and instinctively recognizes Kurome’s name. 23 24 He later develops similar unexplained familiarity with Akame, while remaining certain that he is not native to her world. 36 38

Personality

Koizumi begins directionless and confused, focused chiefly on regaining his memories. Over time, he develops a deliberate purpose: resolve Singularities, avoid burdening his Servants, and become strong enough to fight beside them. 2 20 38

He is observant, cautious, and information-driven. He seeks intelligence on the Imperial Capital, the Revolutionary Army, and possible Servant involvement rather than accepting either major faction at face value. He is careful around unknown threats, but distinguishes caution from cowardice and will deliberately take risks when necessary. 22 37 43

He is protective of people he considers friends, intervening for Kurome despite his missing memories and worrying about Seryu’s indoctrination under Ouka. He treats Remilia, Reimu, and Hata no Kokoro less as distant subordinates than as family, even when their formal Master-Servant dynamic remains awkward. 22 24 25 47

Koizumi has average innate talent by Reimu’s assessment, but compensates through extreme persistence. He trains until exhaustion, accepts instruction from former enemies, and repeatedly pushes beyond his limits. 21 32 38 His Vampire power can alter his demeanor, bringing bloodlust, aristocratic arrogance, and the danger of being eroded into a violent, bloodthirsty Vampire. 19 21 44

Appearance

Koizumi ordinarily has black eyes and a human appearance. When channeling Remilia’s power, his eyes turn crimson and he takes on distinctly non-human traits and an oppressive, blood-soaked aura. 21 35 44

• Scarlet eyes appear in his Vampire state. 19 21
• His Vampire transformation is visibly enough for Reimu to conclude that his race has changed. 18
• His aura in Vampire state causes Akame to associate him with bloodlust and a non-human presence. 44

Abilities & Skills

Master Contracts and Servant Summoning

Koizumi can summon and maintain contracts with multiple Servants, a capacity that surprises other Servants and Masters.

• Initially bears three Command Seals; Yakumo restores one after he has used seals. 8 9
• Has contracts with Remilia Scarlet, Hakurei Reimu, Hata no Kokoro, Yakumo Yukari, and later Serenity Hassan. 18 39
• Supports several Servants at once; Hundred Personas notes that Serenity’s condition and Spirit Origin improve under his contract. 41
• Gains access to portions of contracted Servants’ powers, though he has not mastered most of them. 24 29 38

Vampire Physiology

Remilia’s power grants Koizumi a temporary Vampire form, heightened combat ability, regeneration, and access to Gungnir.

• Is strongest at night. 21 35
• Regenerates injuries sustained in battle with Esdeath. 28
• His Vampire consciousness can drive him berserk or distort his view of humans. 19 21
• He estimates that he has mastered only about half of Remilia’s power. 38
• Human blood and killing further increase the power he can release. 44

Gungnir

Koizumi materializes and wields Remilia’s crimson spear, Gungnir.

• Uses it against Danger Beasts, Hata no Kokoro, and human opponents. 20 21 32 44
• Can produce attacks comparable to a Noble Phantasm, even when not formally deploying one. 32
• A full Noble Phantasm use consumes substantial energy and can send his power berserk. 21
• Channels red lightning-like spiritual energy through the spear. 44

Emotional Perception

Through his contract with Hata no Kokoro, Koizumi can perceive the emotions of nearby people.

• Detects the anger of the crowd surrounding Kurome. 24
• Uses emotional shifts to gauge sincerity, danger, and Serenity’s interest in him. 29 38 39
• Cannot manipulate emotions at Hata no Kokoro’s level. 24

Root Connection and Poison Resistance

After being poisoned by an Assassin, Koizumi connects to the Root Vortex and gains an incomplete connection to Yakumo Yukari’s power.

• The poison’s effects rapidly fade, apparently due to this power. 35
• He can comprehend the existence of boundaries and gaps but not their operational principles. 35
• He believes a Gap might allow escape in a critical situation, but cannot reliably use one. 42
• His immunity to Serenity Hassan’s poison directly leads to their contract. 39

Combat Training and Senses

Koizumi develops through intensive sparring and practical instruction rather than natural expertise.

• Trains with Hata no Kokoro to control Vampire power, spear technique, timing, and combat limits. 21 32
• Spars with Esdeath, learning to follow her movements despite being unable to defeat her. 28 29
• Trains sensory awareness against Hundred Personas’ clones and Serenity’s ambushes. 33 38
• Admits that stealth and assassination are weaknesses compared with his spear-focused fighting style. 48

Cooking

Koizumi displays an unexpected aptitude for cooking.

• Prepares food that impresses Kurome and her friends. 12
• His cooking contributes to his favorable impression on Gin and the others. 29

Relationships

• Remilia Scarlet — His first known Servant and self-proclaimed master. Her power resides within him; Koizumi regards her as family despite her arrogance. 1 2 19 22
• Yakumo Yukari — Ruler Servant who assigns his Singularity mission. She knows limited information about his past, keeps an emotional distance, and is the apparent source of his Root-linked power. 8 35 37
• Hakurei Reimu — Contracted Servant and close companion. Their interactions are teasing and practical; she worries about his health, inexperience with killing, and reckless self-training. 9 29 41
• Hata no Kokoro — Contracted Servant and primary training partner. She supports him when his power destabilizes and develops a strong bond of trust and concern with him. 20 21 32
• Serenity Hassan — Assassin Servant contracted to Koizumi after discovering that he is immune to her poison. She provides intelligence-gathering support and shows intense personal interest in him. 39 41
• Hundred Personas Hassan — Assassin Servant who trains Koizumi in responding to stealth, ambushes, and clone tactics. 38
• Akame — Night Raid ally who feels an unexplained familiarity with him. Koizumi likewise finds her face familiar; they cooperate on the Reias assassination mission. 36 38 40
• Kurome — Friend whom Koizumi instinctively protects despite memory loss. She trusts him, invites him into her life, and worries for him after Esdeath injures him. 11 24 29
• Seryu Ubiquitous — Former acquaintance and Imperial Guard captain. Koizumi sees her as fundamentally misguided rather than evil and tries to prevent her justice from becoming further twisted. 24 47 49
• Chelsea — Night Raid ally assigned to the Reias mission. She teases Koizumi, while he recognizes the tactical value of her transformation Teigu. 40 41
• Najenda — Night Raid leader who negotiates cooperation with Koizumi and authorizes his mission against the Reias family. 35 40

Story Role / Major Arcs

Awakening and First Summoning

Koizumi wakes with amnesia in a destroyed city, is saved by Remilia, and learns that he is capable of summoning Servants. 1 2

Chaldea and the Singularity Mission

Yakumo Yukari brings him to a simulated Chaldea and explains his responsibility to correct divergent parallel worlds by dealing with their Holy Grails. 8

Imperial Capital Investigation

Koizumi enters the Akame ga Kill world with Reimu and Hata no Kokoro, investigates its distortion, meets Kurome and her friends, and experiences further memory loss. 10 15 24

Vampire Training and Night Raid Cooperation

After Remilia’s power manifests, Koizumi trains to master it rather than remain dependent on Reimu and Hata no Kokoro. He eventually enters a temporary cooperative arrangement with Night Raid, where he gains training from the Hassans and forms a contract with Serenity. 19 21 35 38 40

Reias Assassination Mission

To prepare himself for the brutality of future Singularities, Koizumi volunteers for Night Raid’s mission against the Reias family. Accompanied by Akame and Chelsea, he kills for the first time, gaining strength while confronting the influence of his Vampire nature. 40 45

Seryu and the Imperial Capital’s Corruption

Koizumi returns to the Imperial Capital to check on Seryu, exposes the Reias family’s crimes to her, and attempts to redirect her sense of justice away from the Empire’s corruption. 47 49

Trivia

• Fou, who usually approaches only Mash Kyrielight, is unusually affectionate toward Koizumi. 4
• He is uncomfortable with being treated as a mere servant, but often tolerates Remilia’s orders anyway. 2
• Koizumi’s Command Seals are described on different hands at different points: two remain on his left hand in Chapter 8, while assassins identify two on his right hand in Chapter 33. 8 33
• He considers himself a poor fit for stealth and assassination, joking that his abilities are invested in spear mastery instead. 48