I Awakened an Invincible SSS-Rank Gatling Gun

A decade after monsters overran the world, Ethan has nothing left to rely on: no healing serum, no rank, and only his younger sister to protect. Their survival is precarious, and every day brings another threat from the endless horde. When an unexpected power awakens inside him, Ethan must decide whether to reveal what he has become or keep pretending he is as weak as everyone assumes.