Here's Gaueko again, and again in symbolic settings. He won't have anything ripping out of his back like that, for one.
In the Midian-settings, Gaueko has been cursed to be a human along with his son, Kenta (who's the source of the curse). And while he's been around long enough to adapt the necessarily mindset to mingle in with civilization, he still carries the scar on his back he'd gotten from the Forge within The Coils. And while you can't see the scar, the monstrosity that rips from his back stands for the burden he carries, and the illusionary effect it has on anyone that glances at the scar for too long.
The scar in question can't be observed for too long by anything that reads 'sight'. So this doesn't just involve the eye of people or creatures, but devices as well, such as cameras. Anyone who's perceptive to fear will start to hallucinate (which will always involve eyes) in such a way that it triggers fright. When someone looks at a recording of the scar, they'll see the whole room -- or place involved -- filled with translucent silhouettes of people whose faces are obscured by draped fabric. They are the trapped souls of those devoured by Gaueko.