Sean Datz

Name: Sean Datz

Gender: Male

Series: Undead Unluck

Affiliation (first loop): UNDER

Affiliation (new loop): Union

Role: Negator (denier of a natural law)

Negation Ability: UNSEEN (Invisibility)

Voice Actor (anime): Kento Shiraishi

Birthday: June 12

Age: 18

Height: Around 170 cm (self-estimated)

Weight: Unknown (“I never get the chance to weigh myself”)

Hobbies: Collecting hats

Skills: Butterfly knife tricks, pickpocketing, assassination

Favorite Things: Fruit in general, money

Sean is a former Brazilian gang member who used his invisibility-based Negation ability for crime.

He later becomes a coerced member of UNDER, and in the new loop is “rescued” early and recruited into Union, where he grows into a more heroic, if still goofy, ally.

He is classified as a self-target, forced-activation Negator: his ability always triggers under its conditions, even if he doesn’t want it to.

In the original timeline, he is positioned as an assassin and briefly a significant threat, but he dies quickly; in the 101st loop, he finally gets substantial development and becomes a core supporting character.

Sean is a young man with a delinquent, street-thug vibe and a cocky expression.

He typically wears a cap, often backward, which fits with his casual, “bad boy” aesthetic.

In the UNDER timeline, he has a third eye surgically implanted in his forehead to bypass the main drawback of his ability.

He wears his cap backwards so that the adjustment hole lines up with the spot where the third eye peeks through, making the eye visible.

In the 101st loop, he appears a bit younger and softer around the edges, closer in age and demeanor to Fuuko Izumo.

He does not yet have the third eye, and his distinctive fluffy bangs cover his forehead, giving him a less hardened, more “normal teen” appearance.

First Loop: Violent, Arrogant Delinquent

Originally, Sean grows up in Brazil and falls in with a gang that exploits his ability for crime.

He freely uses invisibility for theft and murder and has no qualms about killing, especially when armed with his knife.

He is arrogant, brash, and insubordinate, especially toward Rip Tristan, the UNDER member who forcibly recruits him.

Given that Rip immobilizes him and literally implants a foreign object into his body, Sean’s refusal to obediently listen to him is portrayed as an understandable reaction rather than simple stubbornness.

Sean enjoys using a knife as his main weapon, combining it with invisibility to strike without warning.

He is also susceptible to charm-based negation that excludes those with unwavering love or no awareness of love, strongly implying he is a lustful, impulsive young man with plenty of “impure” motives.

101st Loop: Goofy, Kind, and Trying to Be a Hero

In the new loop, Sean is still a small-time criminal, but he hasn’t yet sunk to full-on murderer.

He’s more of a kid who “got in with the wrong crowd,” using his ability to, for example, steal his boss’s wallet rather than committing brutal crimes.

He is cowardly in real combat at first, freezing up under gunfire and explosions, and even attempts to surrender on the battlefield.

This causes Creed Deckard to label him “miscast,” a painful blow to someone who once dreamed of being a leading man.

Despite his cowardice and ego, Sean is fundamentally good-natured once removed from the worst influences.

He is an easygoing, talkative, somewhat dumb but lovable young man who craves recognition, wants to be “cool,” and desperately wants to matter.

He also has a strong “side character” complex: he tends to think of himself as a background extra who only drags others down.

Fuuko directly challenges this, telling him that he is not a mere extra, but someone who can fulfill his own unique role—and that line hits him deeply as a former aspiring actor.

Relationship with Romance, Friends, and Attention

Sean has a strong desire to be popular and to impress women.

He tries to set up mixers with older Union staff, asks for contact information, gets overly excited in girls’ rooms, and even attempts a “might as well try” confession during a covert mission.

At the same time, his bond with his teammates becomes genuine and warm.

He grows especially close to peers like Gina Chamber and Chikara Shigeno, often acting in a shared trio.

With Fuuko, he develops a deep trust and refers to her affectionately as “brother” (bro), recognizing her as the one who gave him a real place and helped him reclaim his dream.

He also dotes on Phil, partly because Phil loves movies and admires Sean’s father as an actor, which makes Phil feel like a kid brother to him.

By the time of the “Muscle Cloud” test (a flying cloud that only supports the good-hearted), Sean just barely qualifies as a “good person”—his lower body sinks into the cloud.

This visual gag underlines how he’s no saint, but his innate kindness has re-emerged enough to be recognized.

Sean is the son of a character actor father, a man who mostly played supporting or minor roles rather than leads.

Resenting this, Sean grew up frustrated with his father’s lack of stardom and dreamed of becoming a major leading actor who would “show up” his late father.

He harbored a strong yearning for the spotlight, wanting to be at center stage, not in the background.

However, during an audition for the lead role in a movie, his life is changed forever.

In the middle of that audition, his Negation ability UNSEEN suddenly manifests.

Every time he blinks, he disappears from the camera view—an invisible actor cannot be filmed, and the dream collapses on the spot.

Having his lifelong dream cut off so abruptly and unfairly drives Sean into despair and resentment.

In that vulnerable state, he is approached by gangsters who see the obvious value of an invisible man for crime.

They recruit him, and he begins using his invisibility for theft and eventually for violent acts, drifting further and further from his original dream.

Despite this, some part of his admiration for his father and his desire to act never fully vanish; they are simply buried under anger and self-hatred.

In the new loop, thanks to meeting Fuuko earlier in his life, this buried admiration resurfaces.

He comes to realize that “blood doesn’t lie,” and that, like his father, he can embrace a “supporting role” that saves others, even if he isn’t always in the spotlight.

First Loop (Original Timeline)

In the original history, Sean becomes a target of Union, with a mission issued to locate and capture him.

Union tracks him using rewards data, but UNDER, led by Rip Tristan, intercepts and abducts him first.

Rip imprisons Sean and eventually forces him into UNDER through torture and coercion.

Sean’s third eye is implanted to remove the biggest flaw of his ability: the fact that he must close his eyes to activate it.

Sean is later involved in the Autumn battle, where he is supposed to assassinate Fuuko.

In the anime, this assassination attempt is shown explicitly: during the fight with the UMA Autumn, Sean seizes the moment when Fuuko is separated from Andy and tries to slit her throat with a knife while invisible.

In the original, unaltered history, he succeeds and kills Fuuko, dramatically altering events.

However, thanks to the efforts of Un Anno, this future is averted in the current narrative.

Instead, Sean’s assassination attempt fails, and he is ultimately killed by Andy’s attack, cut in half in a quick and brutal scene.

His death comes soon after his proper introduction, giving him a famously abrupt and “invisible” exit from the story.

This brevity became something of a meta-joke among fans and even from the author himself.

He is described as if his Negation were not “Invisibility” but “Unfortunate,” a character destined to be overlooked and mistreated by the narrative.

101st Loop (New Timeline)

In the 101st loop, Sean appears earlier in his life, still a low-level gang punk rather than a hardened killer.

He uses his UNSEEN ability for petty theft, like stealing from his boss, but has not yet plunged into full-blown atrocity.

Union targets him as part of a larger operation to recover the artifact Remember and to gather key Negators from a warzone.

However, Fuuko’s motive for capturing him is not to use him as a weapon, but to protect him from the horrible death he suffered in the previous history.

The capture sequence highlights both his ability and its countermeasures.

UNSEEN does not fool thermal imaging, so Union uses thermography to track him, Gina Chamber’s “Unchange” to seal escape routes, and Void Volks’s “Unavoidable” to restrain him, allowing Fuuko to personally tackle and secure him.

Sean initially refuses to cooperate and believes he’s being pressed into service because they “need his power.”

When he discovers that Fuuko had no intention of forcing him to fight, his ego and curiosity kick in, and he basically invites himself along to the front.

On the battlefield, reality hits him hard.

Gunfire, explosions, and brutal conditions reduce him to a trembling wreck, and he even tries to surrender, earning Creed Deckard’s contempt and “miscast” label.

This moment deeply wounds Sean, who already fears being stuck as a useless bit-part in life.

However, Fuuko rallies him, telling him that he is not a mere extra, that he has a special role only he can fulfill, and that as the Negator of “Invisibility,” he should “return the gaze” instead of looking away from his own potential.

Encouraged by her words, Sean unlocks a deeper layer of UNSEEN.

He stops turning away from his own aspirations and uses his ability in a new, more precise way, helping Fuuko break through Creed’s defenses.

From that point on, Sean formally accepts his place in Union.

He pins the Union emblem proudly to his hat, no longer treating it as something to discard.

He fights alongside Fuuko, Gina, Chikara, and others in later operations.

During the space arc, he even risks himself to help Gina confirm the safety of her “Unchange” pipes in space, acting as the one to physically go and check when she cannot see them.

He also participates in a scheme with Gina to stow away on the rocket headed for space to rescue Phil.

They succeed in sneaking aboard but are understandably chewed out by Nico Vorgeil and Fuuko afterward.

Throughout this loop, Sean evolves from a would-be leading man turned invisible criminal into a supporting hero, someone who proudly embraces being a “side character” if it means saving others.

This arc resonates strongly with his family history and his restoration of respect for his father, the supporting actor.

Basic Nature

Sean’s Negation ability is UNSEEN (Invisibility).

It is a self-target, forced-activation ability that denies the visibility of himself and what he recognizes as his own property.

When both eyelids are closed, Sean and any objects he regards as his possessions become invisible to normal sight.

Clothes and equipment he believes he owns also vanish from sight, turning him into a classic invisible man.

The main drawback is harsh: when he closes his eyes, his own vision is also gone, making him effectively blind while invisible.

This limits his ability to maneuver and fight, since he cannot see where he is going or where his enemies are.

He exploited this power for crime, using it for stealth movement, theft, and lethal ambushes with his knife.

In the UNDER timeline, this ability becomes far more dangerous thanks to a grisly workaround.

Third Eye Implant (UNDER Timeline)

After joining UNDER, Sean undergoes surgery to implant a third eye in his forehead.

This eye remains open while his natural eyes can be closed, allowing UNSEEN to trigger without fully losing his vision.

With this modification, the main weakness of UNSEEN is effectively removed.

Sean can become invisible to others while still seeing through the forehead eye, enabling accurate movement, precise knife attacks, and better stealth.

Visually, the third eye sits under his hat, peeking out of the hole at the back of his backward cap.

It symbolizes how far UNDER is willing to go in exploiting Negators, and how far Sean is forced from a normal life in that timeline.

Ability Extensions in the 101st Loop

Because he meets Fuuko earlier and is guided more gently, Sean develops more nuanced and powerful interpretations of UNSEEN.

1. Selective Invisibility – Making Allies Invisible

He learns to treat his power as “making what he needs unseeable.”

When he regards his allies as “necessary,” he can extend UNSEEN to make them invisible too, as long as:

His eyes are closed (activating the negation).

He is holding hands with someone he truly trusts.

In this state, both Sean and the teammate he is connected to vanish from sight together.

This is especially useful for infiltration, dodging detection, or shielding allies from enemy vision.

2. Invisible Parameters – Erasing His Own “Data”

Under Gina’s coaching, Sean pushes the conceptual boundaries of his ability even further.

Instead of only hiding visible surfaces, he learns to “not recognize” his own physical data, such as body weight.

By no longer acknowledging his weight, he effectively removes it from the world’s awareness, allowing unusual movement, especially in low-gravity or vacuum environments like space.

This interpretation is key during the space mission, where manipulating how the world “perceives” his body helps him function where normal physics would be deadly.

Through these expansions, UNSEEN becomes more than just an invisibility trick.

It turns into a versatile reality-denial power that hides whatever Sean, in his heart and mind, categorizes as “something I don’t want the world to see or weigh.”

Fuuko Izumo

Fuuko is the central figure who rescues Sean’s life in the 101st loop, both physically and emotionally.

She captures him not to use him, but to stop him from repeating his tragic fate, and later encourages him to accept his role and dreams.

Sean admires Fuuko deeply and trusts her completely, calling her “brother” as a sign of closeness and respect.

He sees her as the one who gave him back his “place” in the world, allowing him to stand proud as a member of Union.

Gina Chamber

Sean and Gina are often seen together, and their dynamic grows increasingly warm.

They cooperate in training and missions, including the dangerous space-related operations where Gina helps him refine UNSEEN.

Over time, they develop a subtly romantic atmosphere, especially notable after the Christmas bonus manga material.

Fans frequently pair them as a duo, and Sean clearly values her as more than just a teammate.

Chikara Shigeno

Sean and Chikara Shigeno are similar in age and temperament, making them natural buddies within Union.

They often appear together in team scenes, playing off each other’s nervousness and growth.

Their friendship helps emphasize Sean’s role as part of the “younger generation” of Union.

Together, they bring a youthful, sometimes comedic energy to the group.

Phil

Phil connects with Sean over movies, especially because Phil is a fan of Sean’s father as an actor.

This bond is particularly meaningful to Sean, who once resented his father’s supporting roles.

Because of this connection, Sean treats Phil like a younger brother he wants to protect and impress.

His determination to join the space mission to save Phil reflects that affection, even if he resorts to sneaky methods like rocket stowaway schemes.

Rip Tristan and UNDER

In the original timeline, Rip Tristan is the one who tracks down and captures Sean before Union can.

Rip uses extreme methods to force Sean into UNDER, including torture and the third eye implantation.

Sean resents Rip for this and refuses to obey him blindly, answering arrogance with arrogance.

Their relationship is tense and hostile, shaped by coercion rather than mutual respect.

Creed Deckard

Creed plays a pivotal emotional role for Sean in the 101st loop.

When Sean crumbles on the battlefield, Creed harshly labels him “miscast,” echoing Sean’s worst fear of being an unfit, worthless actor in the story of life.

This insult initially devastates Sean but ultimately becomes the catalyst, when combined with Fuuko’s encouragement, for him to recast himself as a meaningful “supporting hero.”

Defeating Creed’s expectations is part of Sean’s personal victory.

Sean’s original run in the series was extremely short: he appeared, revealed his power, and then was quickly killed.

Because of this, when the first popularity poll happened, his best material had not yet been published, and he ranked poorly, almost as if he were “invisible” in the results.

Fans joked that his true Negation was “Unfortunate” rather than “Unseen,” given how mistreated he seemed by the plot.

The author himself leaned into this, remarking that Sean might be the Negator of misfortune.

His canonical date of death in the original timeline, December 5, 2020 (in publishing terms), inspired fans to create memorial fan art featuring his favorite fruits.

Online, tags like “UNSEEN first anniversary” and “UNSEEN second anniversary” were used to share drawings and tributes.

Within the story, Sean’s arc is heavily tied to the themes of main character vs. supporting role.

As the son of a career supporting actor who tried to outshine his father, he ultimately finds pride in being a “supporting character” who makes the main story possible.

He also has notable similarities to another magazine character, Kusuke Michibata, from a different science fiction series: both are blond, can turn invisible, want to be popular, and have a somewhat pathetic but endearing charm.

This parallel is often mentioned jokingly by readers of both works.