Nocturnal

Slitted verticle Pupils.  
A recessive gene that seems to be expressed as more of a rare mutation within people with Lunarian ancestry.  One parent must have the gene in their bloodline, but it is rarely expressed. Often, neither parent will outwardly have this gene, rather one of their grandparents, or great-grandparents. 
There are mixed feelings about this gene.  People with this mutation have superior vision, especially at night. The nocturnal unit is often highly trained, and almost every mission is equipped with one Nocturnal unit member.  They are almost always elite soldiers, and this is one of the highest statuses in the kingdom of the moons. 
No matter which moon, or what power you wield as a Nocturnal, you are most likely to be trained in the nocturnal school.  They meet at night.  This can lead to social isolation.  They are often pale from the low exposure to light, and have a sleep schedule that keeps them from normal social life.
There are old superstitions, long outdated and not widely believed about nocturnals being evil.  These stories are still culturally relevant as they are still told and lead to some being weary of Nocturnals.  There are also religious discrepancies with the practice of night school and activities.  The night is pretty strictly for sleeping and because of this religious belief, there are those who despise nocturnals.
 Nocturnals are more often than not called "Snakes".  Some see this as a compliment, others as derogatory.  There are two reasons for this nickname of sorts.  Obviously, some snakes have slit eyes.  People who use it positively believe snakes to be cunning resourceful and tricky.  A rarer use of the word tbh.
Many people in the city use it neutrally, as more of a common name without thinking any more or less of the term. Regardless, even some of the neutral users of the term still will find themselves not shopping at a shop run by a snake, crossing the street if they see one coming or not having their children play with a snake.
There are those who purposely use the term snake to mock nocturnals.  There is a definite tone, a condescension, a vial look. 
For the nocturnal population, this is a complicated matter.  A lot of government material signs, documents and such will label them as snakes rather than nocturnals.  This matter became a lot more complicated when the royal family gave birth to a Nocturnal.