Icara is the White Witch of Luculla Forest.
Her cabin is protected by a mysterious barrier, so you must find the Barrier Removal Spell to get rid of it in order to enter the cabin. If you don't want to find the spell, you can just kill the two talking mushrooms near her hut. Without them, the barrier disappears.
She is the elder sister of the plot's main antagonist, Leandra. The sisters have an inborn ability to control the Source - as did their parents, but unlike most sourcerers, they used their magic for healing. One day Source Hunters cruelly murdered their parents while Leandra and Icara witnessed it from their hiding place. Because of the shared traumatic experience, their souls had been forged.
They fled and hid, just living by themselves, tending to the natural inhabitants of Luculla forest and avoiding contact with other people. But one day, a wizard named Zandalor approached them. The trio got along very well but over time both sisters developed strong feelings for the wizard. Being soulforged, Leandra and Icara were aware of each other's affections towards Zandalor. He eventually confessed his love for Icara and together they told Leandra. Grief-stricken, she fled their home and over time their soulforge grew weaker. Later on, if you obtain Soulforge Repair Ritual during the quest A Forge of Souls, you can choose to repair the Soulforge between Icara and Leandra.
At the time when the Protagonists came to Cyseal, Icara has been captured by the Immaculates who follow the Conduit, Leandra. Leandra helped Ice King Boreas seal all other Elemental Kings to bring Eternal Winter on the faery world, Hiberheim, and in return Boreas imprisoned Icara in Ice.
You have to free the 3 Elemental Kings who have been sealed away by Boreas, in order to obtain the Fire Rune from King Sua. The rune is used to summon Sua, who melts Icara's icy prison. After you free her, she accompanies you to your Homestead and assists you in finding Zandalor and stopping Leandra. This time you find out that she is a pupil of Zixzax.