Transformative Weapons

Transformation Weapons are living artificial beings that have what is known as the Transformation ability, which allows them to form and reshape almost any part of their body into a weapon by using the nano-machines in their bodies. The purpose of their creation is to be ordered to kill, so they are raised to be skilled fighters and cold hearted killers. So far there are three who are known as Transformation Weapons and they are a females with the bodies of a child, although they can also reshape there bodies to look more adult like. They're also able to use there ability change there own clothing.

The Organization
The Organization is a secret facility that create these artificial beings, one of the scientists part of the Organization was Dr. Tearju Lunatique who created the first Transformation Weapon and did it with her own DNA thus giving birth to Eve. Tearju planned on giving her happy childhood but the organization had other plans, to raise her as a cold blooded killer by chasing Tearju away and create more to sell those with bad intentions. However the Organization was destroyed by Black and Eve was set free.

Golden Darkness
After the Organization fell, Eve moved on to be a cold and emotionless assassin known as Golden Darkness. She secluded herself from any emotional contact, until she was hired by Lacospo to kill Rito Yuuki, but was convinced by Lala otherwise, so instead she chose to assess him, claiming that she will kill him one day and staying on Earth. By doing so, overtime she finally opens up to humanity and shows a kinder side to herself. She becomes friends with others and starts having love/hate feelings for Rito. She also becomes closer to Tearju again (though she still feels akward around her). She is renamed as Yami, which represents her coming closer to humanity.

Before being set free, the scientists of the Organization placed an ability known as "Darkness" after Tearju's banishment, which she calls "the forbidden transformation". It is said by Nemesis that it caused destruction throughout the Universe and it will activate on its own regardless of Yami's relations on Earth, which has so recently.

2nd Gen-Transformation Weapon: Mea
Some time after the fall of the Organization, in the midst of all the rubble, Mea Kurosaki awoke from suspended animation and the first thing she ever saw was destruction everywhere. While wandering around aimlessly through the place lost and confused, she met Nemesis. After their encounter, Mea greatly respected Nemesis as her master, who raised and taught her about the life of a living weapon and about how Yami is in fact her older sister. Mea does not know much about life outside of being a weapon to kill. She is quite sadistic, childish and low-educated about certain things like sex ed. She came to Earth to bring Yami back to being a cold-hearted killer again and cannot understand exactly why she stayed on Earth and became friends with humans. Mea tries to understand her sister's feelings by becoming close friends with Nana. As time goes by, Mea begins to see the world in a different light and slowly opens up to humanity like Yami.

Project Nemesis
Unlike the previous two, Nemesis is said to have been created by a completely different faction from the organization that created Yami and Mea. It is stated by Tearju that this project was a failure, with Nemesis being the only survivor of the project. What caused its downfall is unknown.

Nemesis
Somehow being the only survivor of this project, Nemesis for some reason headed to the original organization (which was destroyed at the time) and met Mea, whom she took in and taught her about fighting using her abilities and the meaning of their existence, which Nemesis proclaims that it's to kill and having no emotions which would hold them back. She came to Earth with Mea to bring Yami back to her old cold-hearted self. However she claims that she will regardless of her relations on Earth when the "Darkness ability" within her activates.

Trivia

 * A protagonist from an American TV series Generator Rex, has powers similar to the transfomation abilities (creating huge machines and/or weapons from a body part of his) because of the nano-machines in his body known as "Nanites".