Sekirei

Sekirei are an alien race of super-powered humanoids that are physically and genetically indistinguishable from humans. Their name is taken from the Japanese wagtail.

Biology
The physiology of a Sekirei is similar to humans. They have similar requirements such as the need to eat food, drink water, and breathe oxygen. They are also also capable of reproducing with the human species; thousands of years in the past, some Sekirei were able to conceive offspring with their Ashikabi. Due to this, the genes of Sekirei, while recessive, are still carried by nearly half of the world's population.

However, they also have significant differences that set them apart: Sekirei have greater strength, speed, and stamina than is possible for humans. In addition, each Sekirei has a Tama (Core) that is the source of their power and very existence; Sekirei who lose their core cease to function. The Tama is a component of a Sekirei's body also referred to as the Sekirei Soul, Sekirei Core or Sekirei Spirit. Basically, it is the core/nucleus which enable Sekirei to live and use their powers, so in essence it is the life of a Sekirei itself, a Sekirei who loses its Tama ceases to function.

There are two ways to terminate a Sekirei: The first is through defeating them in physical combat by inflicting a sufficient amount and severity of damage; the second is for an opponent to touch the crest at the nape of their neck and recite their Norito. The crest then disappears, indicating termination. A Sekirei whose crest has disappeared cannot function. The severity of physical damage to a Sekirei is categorized in five levels of going from one to five, the former being the most benign and five being the most severe; Damage Level Five is effectively the actual death of the Sekirei.

Powers and Abilities
Despite being similar to humans, all Sekirei have greater strength, speed, and stamina than is possible for humans. In addition, each Sekirei has a core that is the source of their power and very existence; Sekirei who lose their core cease to function. Yet by genetic altercations or born with natural abilities, they can have their own special superhuman powers such as technopath, cryokinesis, gravity and many more. Some will be born with natural talents such as skilled swordsmanship, close combat fighting, acrobatics, weaponry, etc.

All Sekirei have a Norito. Norito is a special power which can be used by a Sekirei after physical contact, executing a kiss with their Ashikabi. A reaction caused by the genes of those with the aptitude to become an ashikabi, causes the wings to be released and the powers, a prayer to become amplified. The Norito is a big element in determining the outcome of a battle between Sekirei. The Norito is basically the only reason why an Ashikabi can be required on the battlefield. It is more or less a type of chant or prayer after kissing their Ashikabi.

The Ashikabi are humans with unique genes that enable them to empower Sekirei destined to serve them through an exchange of DNA between the Sekirei and the Ashikabi (usually done through a kiss). The result is a "winged" (or "emerged") Sekirei with whom an everlasting bond is forged. This reaction is one of deep and committed romantic love and fondness, although some Sekirei may instead view their Ashikabi as one does a friend or sibling. If a person is an Ashikabi they can forcefully wing Sekirei against their will, but this goes against the principle that the Ashikabi's power is the power of fate rather than letting the Sekirei find their destined Ashikabi naturally. In terms of appearance, unlike Sekirei (who are mostly buxom women or handsome young men) Ashikabi can be quite innocuous as they vary in gender, age, sexual orientation, personality, and even social status. The power of an Ashikabi can be determined not only by the number of Sekirei he or she has bonded to him or her, but by the emotional bond between them. One aspect of the bond between Sekirei and Ashikabi is that they can feel each others feelings.