From Human to the Unnameable

(Cthulhu Mythos + nonhuman protagonist + not a selfless saint + not invincible + slow-paced + no female lead)

This is the third weekend without a sun.

At first, Meng Chi merely thought the rain had gone on a little too long.

Until…

The stench of rotten fish began to fill the apartment building.

Waves surged across the sea, and a colossal city rose from its depths.

The blood-red moon suddenly opened countless eyes.

An indescribable being had come from the distant cosmos.

Only then did Meng Chi realize that the rain-soaked city before him was merely the thinnest surface of the truth.

And he himself was becoming… less and less human.

(Note: The protagonist does not begin mutating right away.)