Humanity's App Is Downloading

[Cthulhu] + [System] + [Mythology]

Three years ago, my parents died, leaving behind only a phone.

Three years later, the phone automatically downloaded the Human App.

As a towering tide of blood swept through the city, countless blood-red arms filled the sky.

Anyone drenched by the blood rain turned into a Blood Servant, and the Human App issued a mission:

[Main Mission: Survive

Difficulty: ★★★★★★★★★

Mission Reward: ...]