1. Core World-Building Elements (The Supernatural Reality of Trauma)
*Kyo (also called Hollows)
Distorted pocket dimensions that manifest where ordinary buildings or rooms once stood. They are literal physical expressions of collective or personal trauma. Inside a Kyo, time, space, and physics warp: clocks stop, hallways loop endlessly, objects acquire emotional "weight" that can crush or comfort. A Kyo begins as a simple grief-loop but can "learn" and begin offering seductive false satisfactions (a perfect family reunion, endless love, etc.) to trap victims permanently. When it reaches "critical sympathy," it detaches from its original trauma source and becomes self-sustaining. The official Chiriyaku organization's mandate is to map, contain, or close Kyo before they spread and fracture reality further. Every early chapter (1–13 especially) features a different Kyo as a self-contained "geography" of regret.
*Kegare
The invisible "pollution" or spiritual impurity generated by large-scale national traumas (1995 Kobe earthquake, Aum sarin attacks, 2011 tsunami, etc.). Kegare thins the boundary between memory and physical space, allowing grief to literally expand outward and create Kyo. It is a saturating atmospheric force that accumulates over decades and can fracture the entire country if left unchecked. Exposure leaves a sticky emotional residue that requires ritual cleansing. The entire cosmology of the novel is built on kegare as the raw material that Ren cultivates.
*Fractures
Tears or weak points in ordinary reality caused by accumulated kegare. These are the entry/exit points between the normal world and Kyo or kakuriyo. Ren's ultimate goal is to reach the single central "Kokoro" that lies at the deepest intersection of all fractures.
*Kokoro
Literally "heart/mind/inner core." It is the singular, vast consciousness at the center of every fracture — the ultimate prize Ren seeks. Kokoro is both Ren's aspiration (a god-like heart that could absorb and instantly resolve all national trauma) and his vulnerability. It represents total incorporation: the end of individual grief through complete merger. The late arc (Chapters 45–75) reveals Kokoro as the entity that whispers, advances, attempts assimilation, and finally begins to collapse or evolve under the pressure of the protagonists' non-possessive Kanjo.
2. Personal Powers (Shugiin and Related Phenomena)
*Shugiin
An absolute, trauma-born personal truth that crystallizes into a supernatural ability. It is not learned; it is realized in a single moment of crisis and then defines the bearer's entire existence. It activates involuntarily inside Kyo and cannot be faked or suppressed.
-Sorine's Shugiin: "Michi wa Hiraku" ("The path opens"). Born in the 2011 tsunami debris when she was 16, it allows her to create reachable exits for the trapped by maintaining genuine belief that a way through exists. She uses it professionally to extract people but refuses to use it for her own personal closure.
-Vey's Shugiin: "Ware wa Tatsu Mono" ("I am severance"). Born from a teenage realization in a love hotel, it makes Vey inherently forgettable and able to cut loops, close gates, and leave without leaving traces. It is the perfect "hollow" counterpart to Sorine's visceral belief.
"Kanjo
The unique resonance or "edge" formed when two complementary Shugiin (Sorine's opening + Vey's severance) interact. It is far more than romance; it is a deliberate, maintainable threshold — a shared space that exists precisely because both parties refuse to close or possess it. Ren actively cultivates Kanjo because it is the only force stable enough to open the final gate to Kokoro. In later chapters it evolves into a weapon of resistance: an unpredictable, inefficient form of connection that survives only through distance.
3. Hidden Spaces and Realms
*Kakuriyo
The "between-space" or parallel hidden realm that runs alongside normal reality. It is inhabited by "kami of forgotten things" and reveals suppressed memories when accessed. Entry requires strong Kanjo and deliberate refusal of easy satisfaction. Maintaining kakuriyo access is exhausting and dangerous; it is where the protagonists' most intimate documentation and witnessing occur.
*Topological Grief
Grief that has physically warped space instead of remaining internal (e.g., an endless coffee-pouring loop in a kitchen that was once a mother's routine). These create "presences" that feel like ghosts but are actually architectural — the grief itself has become the architecture.
4. Organizations, People, and Entities
*Chiriyaku
The government-backed organization responsible for all Kyo incidents. They maintain public illusion of normalcy, enforce containment protocols (often euphemisms for destruction), limit civilian contact, and recruit agents with useful Shugiin. Ren has deep influence inside Chiriyaku.
*Zo
Chiriyaku's recruited agents/couriers (Vey is one). They possess Shugiin that allow survival inside Kyo and are trained to document, sever, and extract rather than form emotional bonds.
*Kyo-mimi (Hollow Ears)
An unofficial early-warning network of listeners who monitor distress frequencies leaking from Kyo. They are the "ears" that pick up signals before official Chiriyaku arrives (Chapter 4 is named after them).
*Mirror-mind (Ren / Understanding-Ren)
Ren is the ancient cultivator-entity whose ability is perfect, non-judgmental reflection of patterns, fears, memories, and relationships. He "witnesses" and cultivates situations over decades so that Kanjo can mature naturally. Later aspects are called Understanding-Ren; they absorb predecessors and attempt to harvest the protagonists' evolving bond. Ren is not a villain in the traditional sense — he is a mirror that wants to become the Kokoro that ends all suffering by incorporating it.
5. Tools, Rituals, and Practices
*Ofuda
Simple white paper strips or charms that, when activated, glow with vein-like or map-like lines. They mark exits, anchor reality inside Kyo, open temporary paths, or summon help. Both protagonists carry personal ofuda that resonate with their Shugiin.
*Misogi
Traditional purification ritual (waterfall, long shower, or symbolic cleansing) that washes away the kegare residue that clings after Kyo exposure. Vey performs it religiously to maintain their hollow severance.
*Jisei / Kata
Deliberate ritual sequences or "forms" for intimacy and documentation (introduced in Chapter 15). These turn physical closeness or emotional exchange into structured witnessing rather than satisfaction or possession. The characters agree on exact steps so their Kanjo remains open and non-possessive — turning love itself into resistance technology.
+Additional Recurring Terms (Derived Directly from Chapter Titles and Usage)
-Mukade (Centipede Network): The underground communication system referenced in "The Centipede's Warning" (Ch. 17) and later chapters — a chain of between-people passing messages through kakuriyo.
-Predecessors: Earlier Shugiin users whose fragments Ren absorbed; their stories are geological memories that warn the protagonists (Ch. 27, 63).
-Cultivation: Ren's long-term project of growing human Kanjo into a stable gate for Kokoro — the central antagonistic philosophy.
-Threshold: The core metaphor of the title — the space between hollow severance and visceral belief that must remain deliberately open.