|“||You and I are so alike—young, untested amongst these ... wolves||”|
–A Court of Mist and Fury, Ianthe to Feyre
Ianthe has long blond hair, usually hidden under her blue robe. On her forehead, above her brows, she has a tattoo of the different stages of the moon cycle. She has a set of silver rings that she wears on her manicured fingers. Her typical wardrobe consists of a robe with a belt of limpid stones and a band of silver on top of her hood. In the middle of the silver band is a large blue stone. She is described as very beautiful.
Ianthe is ambitious in terms of ensnaring a wealthy courtier or High Lord for marriage and offspring whether they want her or not. She knows exactly what she wants and will go to lengths to get it including manipulating others and forcing people. She was a benefit to Tamlin in the Spring Court as she was aware of everyone in court and outside of it. She hurt Feyre by always siding with Tamlin and being completely and utterly supportive of the wedding.
Ianthe was born in the Spring Court a childhood friend of Tamlin. Her father was one Tamlin's strongest allies at court and captain of his forces. Around 300 years ago she become the youngest of the twelve High Priestess. Her father had sensed the trouble coming and packed up Ianthe and her two younger sisters and fled to Vallahan and lived there for fifty years while their people were butchered and enslaved.
Ianthe first makes an appearance in A Court of Mist and Fury as a member of Tamlin's court where she acts as a companion for Feyre, she helped plan the wedding and took the role of officiating it.
When Feyre returns to the Spring Court, Ianthe apologizes to, claiming that giving Nesta and Elain to the cauldron was only to spare Feyre the sorrow of seeing her sisters grow old—and that she had to help keep the alliance with Hybern. During the Summer Solstice, she performs a ceremony, but is upstaged by Feyre, who uses her Day Court magic to glow in front of the crowd. This unsettles Ianthe, who scrambles back for control and love from the Court.
A set of keys to the Spring Court Manor is later found missing. It is revealed through Feyre‘s magic that the guard on duty was lulled to sleep by Ianthe, who stole the keys and then unleashed a bunch of Nagas on the Manor to gain attention after the solstice incident. Tamlin struggles to choose between the guard or Ianthe, one having served him and willing to die for him, and the latter being a powerful ally to the High Priestesses. He chooses Ianthe, just as Feyre had planned, and whips the innocent guard. This is what ultimately makes Tamlin’s guard leave his service, and splits the Spring Court in half. Later, when Feyre is about to escape the Court, Ianthe shackles Lucien with controlling magic and assaults him. Feyre overhears their conversation and comes to Lucien’s aide. Feyre uses her Daemati abilities and Ianthe smashes her hand against a rock until it breaks and is cursed to never touch another person against their will again.
However, later in the book, it seems as though her mind was healed by the King of Hybern but she still can’t use her hand. Ianthe kills the Suriel and tries to kill Feyre, but Feyre manages to trap her in the Weaver’s Cottage. It is assumed that the Weaver killed Ianthe because when Feyre meets her in battle, the Weaver is wearing Ianthe’s jewel.
In A Court of Mist and Fury, the first interaction we see between Ianthe and the High Lord of Night is at Feyre’s wedding. When Rhysand arrives to disrupt the wedding, Ianthe backs away from the alter, her face drained of color.
This makes more sense when Rhysand shows Feyre a memory of Ianthe around 100 years prior to the events of A Court of Thorns and Roses, in which Ianthe tries to persuade Rhysand into an alliance. She firstly flirts with Azriel and many of the other males in his court before going after Rhysand. Lying naked in his bed, Ianthe tries to get Rhysand to sleep with her. Her true motives are revealed when she tells Rhysand their offspring could rule Prythian. He continuously refuses her advances until she tries to touch him inappropriately. He then breaks her hand with his magic and tells her to never touch anyone in his court again.
Ianthe shows a continuous interest in Lucien during her stay in the Spring Court, even though he doesn't reciprocate. Her interest in him is due to his powerful lineage and the prospect of conceiving his children. While Feyre was living in the Night Court, Tamlin refused to take part in Calanmai so instead Lucien took his place and at Ianthe's insistence completed the Rite with her. After the fact she assaults Lucien in a forest.