[Revision in progress:
70/127 chapters revised.
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In the year 2157, Earth exists as a nightmare landscape, forever scarred by the catastrophic Sunflare Scorch of 2057. This devastating solar event unleashed three waves of destruction that obliterated civilization: first, electromagnetic pulses that fried all technology; second, intense radiation that triggered horrific mutations; and third, the complete collapse of the ozone layer, which rendered the surface nearly uninhabitable. The planet's temperature rose dramatically, weather patterns turned violent and unpredictable, and ecosystems collapsed across the globe.

From this crucible of devastation emerged monstrous threats that now dominate the Earth's surface. The Crawlers—horrifically mutated humans transformed by the Crawler Plague—stalk the ruins of once-great cities. What makes them particularly terrifying is their retention of human intelligence during the early stages of transformation; they represent an ever-present danger to anyone who dares venture above ground.

These monsters combine traits from multiple creatures in twisted configurations. They range from human-sized to massive Leviathan-class entities and can work together with frightening intelligence to systematically destroy any vessel or settlement they encounter.

Humanity's survivors cling to existence in underground vaults scattered across the planet. The most advanced is Cryo Vault Terminus—a massive subterranean complex built into bedrock with multiple levels of interconnected sectors. These facilities represent humanity's last bastion against the hostile world above, with advanced life-support systems, geothermal power, and cryopreservation technology.

In this desperate landscape, where 90.4% of humanity has been lost and the surface world has transformed into an alien ecosystem, one boy awakens alone in Cryo Vault Terminus. He has been granted access to the Phoenix Core—an advanced, quantum-based AI system created by pre-collapse scientists as humanity's last hope. He represents the culmination of Project Phoenix—a desperate plan to preserve human genetic diversity and ensure the species' survival. With the power of the Phoenix Core at his command, he alone holds the potential to revive the cryopreserved remnants of humanity and begin the monumental task of rebuilding civilization in a world that wants nothing more than to finish what the Sunflare started.
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A/N:

Inspired by FalloutxDemonSlayer

This isn’t a smut-fest or a porn novel, it’s ecchi anime–inspired, relationship-driven survival. The MC starts weak and gets hammered by the world, his growth is earned through trials, mistakes, and hard choices. The story uses a dating-sim style affinity system: relationships must be built and earned before any R-18 scenes unlock. In short: bonds and survival come first; the ecchi moments are consequences of trust, not cheap fanservice.

Additional Tags:
RomCom(Romance/Comedy) | Horror | SliceofLife | KingdomBuilding | Survival | No Yuri | No Netori | No NTR | No Rape | Gore | R18 | Yandare | Tsundere

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i'm alone in this apocalypse vault with 14 girls?