Nemesis

Nemesis (ネメシス, Nemeshisu), also known as Master Nemesis, is a character introduced in To Love-Ru: Darkness. She is a transformation weapon, much like Golden Darkness (Yami) and Mea Kurosaki, but does not share their genetic origins. She is Mea's master, whom she gives orders and uses to observe Yami's changes and recent life. At the beginning of To Love-Ru Darkness, her original plan was to make Yami return to being the heartless assassin she was before arriving on Earth and she convinced Mea that this was the only life they were meant to live as weapons. But after allowing Yami and Mea to pursue and become further swayed by their newfound friendships on Earth, it is revealed that her true objective is to make Yami use a transformation ability called "Darkness", a currently unseen ability unique to Yami. Due to her catalyst-like role in the overall plot, she is often considered the main antagonist of To Love-Ru Darkness.

Because she wants Yami to join her and become an assassin again and wants Rito for herself (as her servant) because of his ability to influence Yami and Mea, Nemesis is essentially also the direct antagonist to Momo's plan to include Yami, various other girls and herself into a harem for Rito.

Her real name is unknown and the name 'Nemesis' is based from Project Nemesis, a weapon project that was organized by the assassin organization that created both Yami and Mea. However, this project, as stated by Tearju Lunatique, was a failure and Nemesis is a survivor from the project.

Appearance
Nemesis is a petite-looking girl with long black hair, golden eyes with vertical silt pupils and tanned-skin. Based on her physical appearance, Rito had mistaken her as a little girl. However, she can change her appearance into anything she desires, such as a crow or a cat, or change her herself into a well-endowed adult woman. She has taken to giving herself cat ears often.

At first she wore a scanty black dress, but she used her abilities to change it into a black yukata (claiming how effective it is in a fight) with a star shaped gap symbol on it (similar to the one Yami and Mea have on the chest of their black gothic clothing) and she has a yellow sash wrapped around her waist. When she changed to black yukata first time she had a cat mask which combine with taichi figure covered left side of her head as decoration.

Personality
Nemesis is sadistic, mischievous, domineering and mysterious. She believes that a transformation weapon's only purpose for living is killing. She is often seen hiding in the shadows observing Rito, his friends, and their daily lives through Mea, until she began to approach them herself. She also has an eery and erotic side to her and finds Rito's shyness arousing and would like to have him as her servant. She said that she doesn't have full control over her erotic personality and would act it on impulse. Upon her first appearance, her erotic tendencies quickly earned an uneasy impression from Rito and a strong dislike from Momo. She can be quite patient, like instead of persuading Yami to return to her old heartless life, she decides to wait until she uses the "Darkness ability", believing that Yami will return to that path naturally and that the "Darkness" will inevitably occur regardless of Yami's relationships on Earth.

History
Nemesis is said to be the only survivor of the tragic failure of "Project Nemesis", a different experiment from the project that created Golden Darkness. Mea remembers that Nemesis came to the fallen organization where she found Mea and decided to raise her. She taught her the purpose of a Transformation Weapon is to kill. She also taught her about her sister, Golden Darkness, whom they came to Earth to bring back into space as who she was before.

Powers and Abilities
Tranformation Ability: Nemesis has the same (maybe stronger) transformation ability as Yami and Mea. She is capable of shape-changing any part of her body due to the nano machines within her. Although the full extent of this is unknown.
 * Hair Manipulation: Like Yami and Mea, Nemesis can also control the movement of her hair, extend it's reach and transform it into any animate objects like a key. It is yet unknown what other kind of transformation she can create with her hair.
 * Body Transformation: Before showing her true self, she disguised as Mikan when she approached Yami, Momo and Rito. Nemesis can also alter her appearance and reshape her body to look more adult-like.
 * Animal Transformation: She can also fully transform into animals, even those much smaller than herself, such as a crow or a cat. This ability is something that not even Yami or Mea are seen capable of doing (although they both have been shown to create partial animal forms). She also uses partial transfomation such as growing a pair of butterfly wings from her back to enable flight.
 * Vocal Alteration/Imitation: In addition to her shape shifting abilities, she can also change her voice to sound just like anyone.
 * Attire Transformation: She is able to transform her clothing, as seen when she switches between a black nightgown and a yukata. She is also seen wearing a maid outfit.
 * Mental Manipulation/Body Jack: It is heavily implied, if not confirmed, that she is able to briefly hijack the bodies of lesser-minded individuals even if they were conscious beforehand. While under such effects, her victims have the appearance of zombies and borrow a fraction of her strength in order to hold their own in battle. It is also shown that she is able to speak through them, as she speaks through Saruyama in order to communicate with Yami.
 * Split Personality Manifestation: Nemesis reveals that she is able to manipulate her own mentality by giving herself an alternate personality, which became known as Mea. She can communicate with Mea within their minds, and Mea herself was not aware that she and Nemesis were the same person.
 * Instant Movement: Nemesis is shown to be able to disappear almost instantly before anyone notices.

Trivia

 * It was hinted that she was the one who had the Demon Sword Bladix end up at the Tenjouin mansion, possibly to show Yami the true nature of a weapon is to fight and injure others.