Ougi Oshino

Ougi Oshino is a character from the Monogatari anime and light novels.

Ougi is a mysterious first year at Naoetsu Private High School. Ougi claims to be the niece of Meme Oshino despite having no known family. While commonly referred to as a girl, Ougi first claims to be a male in Suruga Devil in which they state they are a boy and always have been.

Appearance
Ougi has short black hair, large black irises, and pale white skin. Their most common outfit is a female uniform with long sleeves that hide their hands constantly. Because their irises are drawn black, their pupils are never seen. Ougi can be seen wearing black gloves when their hands are showing.

In Hanamonogatari, Ougi switches to a male school uniform.

It's worth noting that while light novel artwork sometimes depicts Ougi in different clothing such as a black dress, they have only ever been seen wearing school uniforms in the anime adaptation.

Personality
Ougi often comes off as very mysterious. They're rarely ever not smiling and always talk in somewhat a condescending tone.

Especially upon first meeting him, Ougi seems to take an obsessive interest in helping Koyomi Araragi, much to his friends' suspicion. Araragi claims that Ougi somehow causes him to blurt out things without hesitation. He's also commented on them knowing things he never told them.

Ougi claims to have a job of "punishing liars", and the execution of the claim implies it is connected to oddites.

As a "conventional monster," Ougi is an entity which exists solely on lying about its identity. Because she sprung from the subconscious guilt of Koyomi Araragi, her personality is designed to "punish" him with criticism, condescension, and various personal attacks. Ougi Oshino has a particular desire to maintain the illusion that she is the apparition-killing "Darkness," which lends credence to her claim that she "punishes liars." Up until the conclusion of "Ougi Dark," her motivation is to sabotage and destroy the hypocritical aspects of Koyomi Araragi's personality, allowing his existence to become more "right."

Trivia

 * Ougi's gender seems indeterminate. In Hanamonogatari (Suruga Devil), Suruga refers to Ougi as 'Ougi-kun', 'he', 'this guy', and 'the boy'. When Suruga asks about it, Ougi tells Suruga that they have always been a boy since they were born, though later Ougi says "Whoops, that's right. I'm a boy now". It's likely that either Ougi, as an oddity, is able to change their body at will, or rather Ougi is just dressing up as a boy, imitating Araragi while helping Kanbaru.
 * The music that plays when Ougi is first shown. Translated, this means something along the lines of 'The woman who was the fake/sham itself'. This namesake eventually becomes wildly appropriate as it is revealed that Ougi is an apparition whose entire personal identity is a fabrication, from her behaviour and responsibilities, to her name and relationships.
 * Ougi's first name uses the kanji for "Fan", which is referenced in the cover artwork for the first volume of Owarimonogatari. The significance of Ougi's name is related to the design of astronomical cartography, as maps of outer space are drawn in a fan-like pattern--which relates to her fabricated identity as a person who upholds rules and order in the universe. Likewise, when she was first introduced to Koyomi Araragi by Suruga Kanbaru, she was explained as being a "fan" of Suruga's basketball.
 * Ougi's traits, character quirks and design and behavior seems to be based on the Carl Jung's Shadow Archetype. The reveal in Ougi Dark seems to support this.
 * "Spooky Ougi" is a common in-joke nickname for Ougi in the western community. The name is a reference to an internet picture depicting a Cat Soup styled Ougi from Owarimonogatari as "The Spooky Ougi of Cute".