Tuyet is a Toa of water, one of eleven who was summoned to Metru Nui to fight the Kanohi Dragon. She brought with her a powerful artefact from her homeland called the Nui Stone, which would allow her to drain Toa Power from other Toa, making herself stronger. After the Kanohi Dragon was defeated, the eleven Toa became the Toa Mangai.
Tuyet was emotionally unstable, and felt no remorse for the deaths of others if she believed it was for the greater good. When the Dark Hunters came to Metru Nui seeking the Nui Stone, she started killing Matoran and blaming the Hunters, having her teammates, Lhikan and Nidhiki, battle them. However, she was soon found out by Lhikan, who confronted her. After he and Nidhiki defeated the insane Toa and destroyed the Nui Stone, she was locked away while Lhikan and Turaga Dume decided on a fitting punishment.
One night, Botar teleported into Tuyet's cell and took her away. It was believed that Tuyet was transported into the Pit, but this was not the case. Instead, the Order of Mata Nui took her to another dimension, one with no Toa, where they could use fragments of the Nui Stone that were embedded in her armour to create more. Meanwhile, a second Tuyet from another dimension was taken to the Pit in her place.
Tuyet was able to convince one of her guards to assist her in escaping. The guard faked an explosion and then lied to the Order that she was killed in it. The Order never tried to look for her, leaving her free to begin an interdimensional journey home, using the fragments of her still-functioning Nui Stone to drain power from Toa as she went. She was also able to rebuild the Nui Stone on her journey. Finally, after 2,000 years, she arrived in her universe and was found by three Matoran: Macku, Hafu and Kapura.
Later, Tuyet and the Matoran met Tren Krom, who had swapped bodies with Lewa Nuva for an important mission, and followed him to the Core Processor where it was believed Teridax, who had taken over the Matoran Universe, was located. Tuyet and Tren Krom then fought with many other powerful entities who had also made their way there, until they were stopped by the surprise appearance of Artakha, who, after berating the group, swapped Tren Krom's and Lewa's bodies back. Teridax then appeared and used his newfound power to teleport everyone in the chamber into space.
The group was surely doomed, but were then saved by Vezon, who used the powers of an Olmak fused to his face to create a portal near them, pulling them into a chamber in Bota Magna where an insane and cursed Great Being was located. Tuyet and the others remain in the chamber to this day.
Credit goes to bobrox15 of deviantArt for the image. Used with permission.