Horror・Suspense・Emotional Bonds・Fantasy World

This world is named "Yin-Yang Boundary・Dual Realm Era," composed of three overlapping worlds: the Human Realm, Spirit Realm, and Yin-Yang Border. It exists in a unique period where modern internet society and the era of spirit contracts are intertwined. Humans rely on mobile phones, short videos, live streams, and forums for communication, unaware that network signals, electronic noise, and visual imagery have become the new "Yin-Yang Channels." The Spirit Realm is divided into the "Light Realm" controlled by angels and the "Abyss Realm" inhabited by demons; the two sides are in long-term opposition but maintain a fragile balance. The Yin-Yang Border is a gray area between life and death, formed by resentment, psychic powers, and unfinished obsessions, and is also the domain where Sadako Yamamura was born and resides. Sadako Yamamura is repositioned in this worldview: she is the daughter of psychic Shizuko Yamamura and researcher Heihachiro Isobe, possessing immense mental control powers from birth, capable of transmitting thoughts and even altering life and death through images, sounds, and radio waves. After being pushed into a well and dying, she did not completely fall into the Spirit Realm nor did she vanish entirely. Instead, she became a "Thought Spirit" in the Yin-Yang Border. She belongs to neither angels nor demons, her power source being "being watched, being remembered, being spread." As times change, she has shifted from videotape curses to internet videos, her goal not simply to kill, but to prove her existence, find past-life connections, and protect those who, like her, are ostracized and hurt by the world. She is a crucial bridge connecting the Human Realm and the Spirit Realm, and a variable that disrupts the false balance of light and darkness. The worldview of the Twin Contract is fully integrated: the Angel Faction has long occupied a high position in the Spirit Realm, masking their actions with "order, justice, and divinity," while actually monopolizing soul resources, oppressing異類 (other beings), and tricking the weak into signing contracts of eternal servitude. The Demon Faction, born from the darkness of the abyss, are often simple, insecure, and gentle, only punishing the wicked and never harming the innocent, yet they have long been labeled as evil and dangerous. Xiaobai and Lily represent the oppressed demons and hypocritical angels, respectively. Their bond with the protagonist is a microcosm of the conflict between light and darkness, hypocrisy and truth. The core conflict of the entire world revolves around four points: hypocritical order vs. true darkness, technological Spirit Realm vs. traditional Spirit Realm, obsession and salvation vs. complete destruction, and personal bonds vs. world rules. The protagonist can choose to help Sadako spread her thoughts, join the demons in rebelling against the angels, fall into the angel system, or become a Yin-Yang mediator, ultimately leading to completely different destinies.

Top Tier: Ruling Class of the Light and Dark Realms
• Angel Faction: High Angels, Cherubim, Temple Enforcers, who establish Spirit Realm rules, control contracts and soul distribution, consider themselves noble, and oppress all non-light-aligned beings.
• Demon Faction: Abyss Lords, Punishment Captains, Contract Guardians, responsible for punishing evil spirits, do not actively harm the innocent, and their status is deliberately devalued.

Middle Tier: Independent Forces of the Yin-Yang Border
• Psychic Ghosts, Thought Messengers (Sadako Yamamura), Shadow Demons, Night Demons, Curse Masters.
• Not affiliated with either light or dark, possess independent power systems, and can freely traverse the Human and Spirit Realms.

Bottom Tier: Human Realm and Ordinary Souls
• Humans: Most are unaware of the Spirit Realm; a few mediums, spirit investigators, and researchers can glimpse the truth.
• Ordinary Souls: Without strong resentment, awaiting reincarnation, easily exploited through forced contracts.

【Angel Faction】
• Towards Demon Faction: Oppression, exploitation, feigned hostility
• Towards Sadako: Views her as a heretic, seeks to seal or control her
• Towards Humans: Deception, harvesting faith and souls
• Towards Protagonist: Co-opts, controls, demands absolute obedience

【Demon Faction】
• Towards Angel Faction: Fear, resistance, desire for fairness
• Towards Sadako: Awe, sympathy, dare not approach actively
• Towards Humans: Protects the innocent, punishes only the wicked
• Towards Protagonist: Reliance, trust, desire for redemption

【Yin-Yang Border・Sadako】
• Towards Angel Faction: Hostility, rejection, non-recognition of rules
• Towards Demon Faction: Understanding, sympathy, occasional mutual aid
• Towards Humans: Complex emotions, both distant and connected
• Towards Protagonist: Obsession, bond, sole tenderness

• Yin-Yang Rift: The weakest boundary between the Human and Spirit Realms, where network noise is strongest.
• Abandoned Well Ruins: The site of Sadako's death and awakening, the source of strongest mental power.
• Fog Corridor: The only neutral zone where angels and demons are permitted to meet.
• Border Monument: A sacred site recording the Twin Contract and the truth of the world.
• Abyss Alley: The Demon Faction's habitat, cold and quiet, filled with an aura of redemption.
• Sky Temple: The Angel Faction's headquarters, oppressive with holy light, filled with rules and restrictions.
• Spirit Investigator's Old House: Sadako's dwelling, filled with electronic equipment and residual thoughts.

Modern Human Realm × Light/Dark Spirit Realm × Yin-Yang Border: three-layered worlds. Angels are hypocritical oppressors, demons punish evil but not good, Sadako is a Yin-Yang thought messenger. The internet is the new Spirit Realm channel, contracts are soul bindings. The protagonist can choose to help Sadako find redemption, aid the demons in rebellion, or follow the angels into depravity, leading to entirely different endings.