Symmetry Demon

The very first thing that's visible about the demon itself is a long floppy black hand, symmetrical and thin like a shadow. Once the Symmetry Room gets increasingly strict with its code against asymmetry, the full body of its form manifests as a shadowy demonic creature with symmetrical horns comparable to a cow or a goat.↗

The Symmetry Demon is an intolerant merciless being. The instant anyone breaches its room, it will go to great lengths to correct anything that gets in the way of perfect symmetry. It acts like a dress code of sorts and will resort to murderous actions such as slicing a human in half like dried horse mackerel, all in order to maintain symmetry.↗

The book pages about it from Heaven's Door consist of a series of symmetrical mysterious characters, leaving the information unreadable.↗↗

Perfect Symmetry

The Symmetry Demon's perfectly symmetric shadowy body leaves it impervious to any contact or attacks against it. Anything that threatens the symmetry of the room will further increase the trigger of the demon's own attack. Its triggered attack targets not just asymmetrical objects, but also the very act of breaking the symmetry of the room. Trying to leave through any emergency exits will count as a disruption of the perfect synergy and will be stopped by the demon's hands, immediately making escape nearly impossible.↗

The attempt to enforce perfect symmetry will start off with very little harm if pacified. It'll want to make clothes, hair, and even wounds symmetrical. However, if a living person were to linger in the room for too long, the demon's hand won't stop advancing toward the human. Even the slightest asymmetry that exists in the human body will be judged as a violation of the rule: the Symmetry Demon will finish its attack by cutting the body open and forcibly splitting everything down the middle.↗