Long ago, Nineko lived alone as an orphan and had to steal from other people. One day, she was caught stealing by the First Spinjitzu Master. Although she stole from him, the First Spinjitzu Master offered Nineko to train her.
Sometime after Nineko turned eighteen, the First Spinjitzu Master noticed that one of his katanas were missing and accused her of stealing it. Ninkeo tried to tell him that she didn't steal it, but he wouldn't listen, so she left and swore that one day she would be stronger than the First Spinjitzu Master and proved to him that he should've believed her.
At first, Nineko tried to perfect Spinjitzu on her own, but soon learned that the only way that she could be better than the First Spinjitzu Master was by becoming immortal. So she studied Dark Magic and used her new abilities to drain the life out of the crops from Komala's village. But due to the spell backfiring, Nineko instead caused the crops to turn black and die.
Because of Komala's spell, Nineko used dark magic to transform herself into a cat, so she could steal the jewel's powers. After turning into a cat, Nineko created a martial art called Catjitzu and practiced it for 10 years. Nineko was able to persuade other people to get the jewel for her, while at the same time, create monsters to get it, but both groups failed to get it because of the Order of Felis.
At the age of eighteen, Nineko had long black hair with a bangs and wore a distinctive make-up. She wore a simple kimono with a neckline.
After being transformed into a grey cat, Nineko retained her slender human body, but her head completely transformed into a cat's head with large yellow eyes. She wore an earring in her right ear. She also kept her long black hair and mostly wore it in her tail fastened with her mallets. She wore a kimono with depicted paws, and pants with a tail sticking out of it. Sometimes she also wore a ninja-hood on her face and sometimes she also wore an another pale green kimono with a skirt with a pattern of blue fish printed on it.
Nineko was once an orphan and had to steal to make a living. When the First Spinjitzu Master took over, she was happy to have a home, but when her master accused her of stealing his katanas, she realized that he would always consider her a thief, so she left him. Gradually, she became much more bitter and longed to be even more powerful than the First Spinjitzu Master. With the help of Dark Magic, she turned into a cat just to get the Cat-Eye Jewel that would guarantee her what her former master had - immortality. Nineko tried to achieve her goal in various ways, ignoring and hurting other people. She even summoned various monsters to get the Jewel for her, but without success.
Later, she was willing to deceive Wu and Garmadon and use their naivete to steal the Jewel, but she was completely indifferent to them, and all she really cared about was achieving immortality.
- Dark Magic: After leaving the First Spinjitzu Master, Nineko learned how to use Dark Magic.
- Permanent shapeshift: Using Dark Magic, Nineko has permanently turned into an anthropomorphic cat.
- Summoning monsters: Using Dark Magic, Nineko can summon monsters from various parts of the island of Ninjago.
- Living hair: Using Dark Magic, Nineko can revive her hair to fulfill her tasks.
- Control over beings: Using Dark Magic, Nineko can curse anyone to accomplish her tasks, although the cursed may take precedence over the original target of her command before furthering her mistress.
- Creating the Warriors of Felis: Using Dark Magic of her umbrella, Nineko can create rain cats called the Warriors of Felis.
- Catjitzu: Using a special form of Spinjitzu, invented by herself, Nineko can walk on ropes, jump high and down without any sound.
- Nine lives: After turning into a cat, Nineko gained eight extra lives.
Behind the scenes
- She seems to be based on Lena Dupree and Simone Lenoir from Scooby-Doo on Zombie Island, two women whose true form was a humanoid cat called a werecat and whose main goal was to achieve immortality through magical practices.
- It is unknown how old she is, but since she destroyed crops in a village when Komala was a little girl, it means that the First Spinjitzu Master trained her several decades before Wu and Garmadon's journey.
- She is similar to Aspheera, as they are both non-human sorceresses who wanted to take revenge on their teacher in some way. Both also abused Wu and Garmadon by helping them in some way and demanding a favor in return. The difference, however, is that while Aspheera required the brothers to teach her some martial art, Nineko did the opposite.
- She is the sixth villain who knows Spinjitzu. The others being Garmadon, the Overlord, Techno Wu, Doubloon and Aspheera.
- She is the fourth main female villain after the Preeminent, Harumi and Aspheera.