Violet is one of the Sakura Five that didn’t make it into the game.
She was the Alter Ego of purity.
In her mid-twenties, she was the oldest of the Sakura Five. She is the adult version of Sakura. She has long hair, a tight fitting battle uniform, and has a taciturn, intelligent aura.
Her job is on the far side of the Moon, at a place that could be considered to be like the Moon’s Ministry of Finance. Sent out by BB, she is responsible for managing the Moon’s resources (Mana). Like the governor of a massive bank and its vault.
She doesn’t have any strange id_es skills (like fetishism) like the other Alter Egos, as an individual her degree of completion is extremely high.
Purely based on impression, she is more like a Servant than an Alter Ego.
She is very pure, therefore we made her motif attachment and desire to monopolize [someone’s heart]. She is a kuudere, so she is very taciturn and cold to others. She is your typical strict manager.
She named herself simply “Violet,” this shows that she has much less desire to play around compared to the other Alter Egos.
Violet is the Sakura of purity, so she doesn’t speak or act in a inflammatory way. It’s also not like she has zero interest in the protagonist either. Conversely she wants to monopolize the protagonist and make them her own. She just wants a “clean, pure relationship.” It’s not too much to say that she is the one who is protecting public morals on the far side of the Moon.

Her id_es skills are “Shackling Desire” and “Crack Ice/Andromeda.”
She has the desire to bind her target and herself in chains, but she keeps this desire secret.
It goes without saying, everyone around her already knows about it. Like, her weapon is a whip for God’s sake!
Crack Ice refers to her mystic eyes that paralyze a wide area. Not just her target, but literally the entire space is charmed by her eyes. In short, it’s like she can stop time.
She was supposed to be a “Good Alter Ego” who would eventually becomes the protagonists ally, and protects the other Masters until the end.

Fate/EXTRA Material: Encyclopedia of Fate/EXTRA