Yua

Yua is the banshee captured and imprisoned by Ari of Arkhanta.

Legend of the Banshees
Banshees are feared evil spirits that dwell in swamps and attempt to lure humans to their demise.

According to legend, a captured banshee will grant her captor three wishes in exchange for her freedom.

Capture and Imprisonment
When Ari's son Maqi was born, he displayed "silent and solitary" behaviour. He did not play with other children or speak, and so Ari set out on a journey to find a cure for his son's mysterious affliction.

At a loss after visiting scholars and physicans and knowing the legend of the banshees, Ari captured Yua, but learnt that she did not have the capacity to heal his son and could only grant material wishes. After wishing for a house and riches for his son, Ari tricked Yua into becoming his eternal servant through his third wish.

With Yua's powers, Ari became Lord of Arkhanta and turned it into a prosperous land.

Yua remained in a guarded water prison in Ari's house, the Scarlet Citadel, until the combined powers of W.I.T.C.H and Orube  freed her.

Freedom and Revenge
Since the Oracle believed it to be unjust and dangerous for Ari to control such immense power, one the Guardians' tasks was to free Yua.

After being freed, Yua, bitter and angered by her imprisonment decided to take revenge on her captor by capturing his son and taking him back to the swamp. W.I.T.C.H. was, however, able to save Maqi and their selflessness deeply touched Yua, disproving the belief that banshees are completely heartless.

Trivia

 * Banshees are part of many folklore stories and mythologies.