Monoeye

The Monoeyes (単眼種 (モノアイ)) are a humanoid Liminal species that possess the notable feature of having only one eye.

Monoeyes are able to see objects up to 2 kilometers away without assistance; however, they have poor depth perception, making it difficult for them to navigate 3-dimensional spaces, and their eyes require constant protection from harsh environments as their size makes them susceptible to dryness and allergies.

Physiological Attributes

 * Sensitive eye: Because the Monoeye's eye is so large, they dry out easier than humans, as well as more likely to get something caught in them, and require a lot of eye-related medication.
 * Visual perception: While Monoeyes have great long-distance vision, their depth perception is very low due to their single eye. It is common for Monoeyes to run into poles and be overall klutzy because of this.
 * Monoeyes are typically socially sensitive about their eyes, and resort to hide them, though ironically, the methods they use to hide their eyes only bring more attention to their face.
 * Monoeyes can order special glasses to hide their eyes, though they are very expensive and not very flattering.
 * Tear ducts: Monoeye tear ducts are proportionally larger than a humans due to their single eye, and they emit tears rather easily to help prevent dry eye as a result.
 * Breasts: Monoeyes, compared to other species, are rather lacking in breast size by average, with notable exception of their Cyclops subspecies.

One-Eyed Priests
The One-Eyed Monk (一つ目入道) subspecies are Monoeyes who have converted to Buddhism. Aside from their mute status, they appear no different than the standard Monoeye, aside from the fact the glances they get from their single eye doesn't trouble them. However, because of this, they are very serious and can be hard on not only themselves, but on others as well.

They mainly use their eyesight to spot those who have neglected their training.

Cyclops
Cyclopes (サイクロプス) are an unusually large Monoeye subspecies, whose special talents lie in smithing/metalwork. Their large eye allows them to accurately determine the temperature of the fire and iron, which is the source of their unique smithing techniques.Also unlike other subspecies, they are surprisingly well-endowed. Other Monoeyes view their special gifts (especially their breasts) with envy.

A rather well-known subspecies, they have been featured throughout popular culture.

Backbeard
Backbeards (バックベアード) are a strange yet powerful Monoeye subspecies. They are capable of hypnosis by having someone stare into their eye, blind others with their glittering eye, and can even fire ocular laser blasts.

As a sacrifice to owning such great abilities, they have juvenile-like bodies, which can result in them being treated like children, a point of discontent for any Backbeard. It is because of this that Backbeards are incredibly suspicious, to the point of calling someone a "lolicon" and run in the opposite direction if someone shows them even the slightest of kindness.

In the Manga

 * Manako

In the Game

 * Ai

Trivia

 * The One-Eyed Monks are the only Monoeye subspecies that uses kanji.
 * They are also based on the Youkai of the same name.
 * The "Backbeard" is based off of Beako; a popular Meme-character from Futaba Channel (2chan) and the de-facto mascot of the Sankaku Complex imageboard, who in turn is based on longtime GeGeGe no Kitaro antagonist Backbeard.
 * Most translations, prior to the revealing of subspecies, had translated "Monoeye" into "Cyclops".
 * In ancient Greek and Roman mythology, other than the giant-sized cyclopes, they cited another tribe of one-eyed people known as the Arimaspi (lit. One-Eyed), stated to be the same size as humans, similar to the Monoeyes. Due to the obscurity of the arimaspians in media, it may be just a coincidence and the name Monoeye sounded easier to associate.
 * Strangely enough, Monoeyes have two eyebrows, however, it serves to make them more expressive.
 * Cyclopes in classical art also had two eyebrows, but their single eye was positioned on the forehead, with skin over where the eyes should be, purposefully misleading that they had two eyes.
 * As revealed in Chapter 3 of Monster Musume: Monster Girls on the Job!, there was indeed a lot of strong discrimination against Monoeyes for a long time, but the ongoing cultural exchange has meant that this discrimination has greatly decreased.