Daughter of the mad Toa Sanguinus, Kidra’s strange destiny brought her through strife and conflict, serenity and sin.
Kidra was born through the fusion of Sanguinus and a Ce-Matoran on Spherus Magna. Her mother was a healer from Artakha who ended up devoting her life to helping the old and battleworn toa recover from the events of Teridax’s reign. Sanguinus was lucid enough to understand there was only so much she could do, however, and after the Ignika granted the matoran species the ability, sacrificed hismelf to bring Kidra into the world.
Growing up in the city of Bazryghan around the old island of Korrothis, Kidra was friends with another matoran named Kazuman. Kazuman combined the Ta-Matoran fascination with forging and the Ko-Matoran desire to decode the workings of the universe, and became a Kanohologist.
Unfortunately, as the guardians of Bazryghan, the Knights of Spherus Magna, became more and more corrupt, they put laws in place to preserve the “holy” old technologies of the Matoran Universe, and persecuted those who tried to create anything new. Kazuman was captured, prompting Kidra to immediately join sides with the rebel faction known as The Druids. She vowed to rescue him.
One of her missions was to capture an ancient Great Being robot known as The Decipherer. With a team of five others, she succeeded. When the Decipherer was cornered, however, he froze the other matoran in time and brought Kidra close, studied her. He explained that he would be neither on the side of the Druids or the Knights, and that his Duty called for him further in the future. He also detected Kidra’s dormant mercury powers. She fell unconscious. When she awoke, she was a toa. She and all of her squad were back in the Druids’ base in Bota Magna.
As a new toa, Kidra should have been sent to the Elemental Council for training, but as the Druids opposed the council, she was instead trained by several of the Druids’ members. This included Ackar, Gloriana, Telzira and many others. Kidra was adept at stealth techniques and was paired up with a couple of Dark Hunters to take on covert missions against the KoSM. Kazuman and Kidra were eventually reunited (though she was not on the mission that rescued him) and lived together after the formation of the new Matoran Empire.
**Kidra was built in 2011**, and is another "loaned" character in the ***Cyclic Plane Storyline***.
The original Kidra was made by Toa Atraks:
Much of this MOC’s build was experimental, with mixed results. The use of trans-purple on the MOC was both to show it off (this was back in 2011 after all…) and because mercury thingies shine purple. Idk. Purple! 
<- Toa Atraks’ Kidra. The character is his.