Summary:

In a sealed briefing hall beneath Border HQ, every squad, strategist, and senior officer gathers for what they are told is a “critical strategic review.”

The lights dim.

On the vast screen in front of them does not appear a simulation, an invasion report, or a training replay. Instead, they see the life of one small Neighbor girl, from the moment she runs laughing across a foreign battlefield to the day she first walks into Mikado City with a shabby coat, a quiet smile, and secrets that could rewrite everything Border thinks it knows.

Her name is Yūma Kuga.
In this world, she is a girl.
On this day, she is no longer a mystery.
She is the movie.

An experimental Trion projection system, recovered from the Neighborhood and refined by Tamakoma, does what no interrogation, no scout, and no databank could achieve. It reconstructs memory as living image and sound, turning the past into a vivid, undeniable record. Every agent in Border is now a captive audience to Yūma’s childhood, her father, the war that stole her body, and the quiet, stubborn courage she carried into their city.

Tamakoma watches with clenched fists and wet eyes.
Kō Murakami, Masato Kageura, Suwa, and Arafune trade shocked whispers, sharp questions, and rough‑edged jokes that fail to hide how deeply the images cut.
HQ listens, cornered by truth. Guilt and regret sit beside a growing respect that feels uncomfortably like reverence.

This first book in the “Watching the Red Trigger” series is framed as the first full “screening” of Yūma’s hidden history. Each chapter unfolds in two layers: the raw past projected on the wall, and the present‑day reactions of the people who once thought they understood her.

Chapter by chapter, Border witnesses:

• A fragile peace in a distant world
They see girl‑Yūma before she ever set foot in Mikado. Small, white‑haired, and sharp‑eyed, she grows up in the shadow of her father, a wandering warrior whose smile is as gentle as his judgment is firm. The screen fills with their everyday rituals: shared meals, quiet lessons on tactics and morality, playful sparring that blurs the line between game and training.
In the viewing room, Tamakoma members and rookies alike feel their expectations crumble. Yūma was never simply a “Neighbor weapon.” She was a daughter, a student, a child who learned to balance kindness with calculated survival.

• The slow tightening of war
Peace frays. Rumors of conflict, the shimmer of gates, and the subtle preparation of their small unit creep in at the edges of the projection. Yūma’s father trains her harder, explains more about Trion, politics, and betrayal, yet shields her from certain truths.
On the other side of the screen, captains and tacticians unconsciously lean forward. Kageura and Suwa mutter their own battlefield judgments. Murakami and Arafune measure Border’s training against what they see here and find it wanting. HQ silently realizes that, long before she arrived, this girl was living at a level of risk and discipline that would break most C‑ranks.

• The choice that costs everything
The war breaks fully into view. Skirmishes turn to decisive battles. Yūma, still young yet terrifyingly capable, is thrust into situations no child should face. One desperate choice to save a life triggers a chain that ends with the slow, merciless failure of her own body.
They watch the moment when experimental Trion technology keeps her alive while stealing her human form. The scene of her father’s sacrifice lands like an explosion in the dark auditorium.
Characters in the watching crowd do not react as soldiers. They react as human beings. Some attempt to argue about tactics or risk, but their voices fray against the raw grief on the screen. HQ officials feel the first sharp stab of personal responsibility; Tamakoma’s members can no longer tolerate the old habit of calling her “just a Neighbor asset.”

• The wandering ghost girl
After the war, they see Yūma travel between worlds like a ghost with a beating heart of Trion, half alive, half lost. Her body is artificial, but her loneliness is devastatingly real. Replica guides her, but cannot replace what she lost.
Border agents watch the small, almost wordless scenes: shared food in strange markets, close calls, the careful way she appraises strangers without ever expecting safety. It is here that respect begins to bloom openly among the watchers. The girl they fought beside, measured, or even dismissed, carried more weight than any of them imagined.

• The first step into Mikado
Finally, the projection reaches her arrival in Mikado City. She steps into this new world not as an invader, but as a tired traveler following fragile instructions from a father who is no longer there to protect her.
Border sees its own city through her eyes: crowded, careless, oddly peaceful compared to the places she survived. They know what comes next in their own timeline, but they have never understood what it cost her to get here.

Every pause of the recording becomes a crucible.
Osamu, Chika, Jin, the Tamakoma branch, the elite attackers and snipers, and even the most hardened HQ officers are forced to confront a simple, brutal fact: they built strategies and policies around a girl whose story they never once tried to truly learn.

This book does not rewrite the events fans remember. It slides the camera behind Yūma’s red Trigger and leaves it there. The canon battles and familiar milestones are still to come in later volumes, but here the focus is on the making of the person behind every decision, every blow, every smile.

“Watching the Red Trigger: How Border Discovered the Girl Behind the Weapon” is a character‑driven, emotionally intense re‑vision of a familiar world. It explores war, family, sacrifice, and the quiet strength of a child who was never allowed to be only a child. It challenges the organization that welcomed her late and judged her early to reckon with its own blind spots.

By the time the credits of this first “movie” roll across the briefing room wall, one thing is painfully clear:

Border did not simply gain a powerful Neighbor agent when Yūma Kuga walked into Mikado.
They inherited the unresolved cost of her survival.
And they can no longer pretend they did not see it.