Hanyō

A is a mixture of a human and a yōkai, either by birth or by unnatural means. There are two ways that a hanyō is born. One can be born of a yōkai and a human. Apparently, in most cases, the father is a yōkai, and the mother is a human.The other way is when a human with an unfulfilled desire merges with many demons; Naraku and Sara were born as hanyō in this fashion.

Physical appearance
Many hanyō by birth show physical signs of their yōkai roots, though they usually have a primarily human appearance. If the children of Hōrai Island are the standard for "normal" half-demons, many of them seem to have pointed ears. And also hanyō which have no physical yōkai-features, almost always have an unusual color of the hair and eyes, or even the skin. Jinenji's mother once said that there is for every pretty half-demon also one which is not it. However, so far Jinenji is the only hanyō which looks "monstrous" in the series.

The unnatural type of hanyō almost have complete human forms due to being originally human however their true form is mostly an amalgamation of other demons put together because they are essentially than a colony of demons inhabiting a human body.

Social Outcast
Due to this mixed nature, hanyō are often considered outcasts to both human and yōkai societies due to the mutual hate between both humans and demons. The humans only see half-demons as no different than the monsters full demons are, while full demons see them as an impure mockery to their demonic powers and thus consider them too weak to associate with. This disdain can lead to unfair prejudice and even downright death threats.

The only people of either races that are even capable of accepting or tolerating hanyō are close family members and/or friends most of the time, who are ostracized themselves for choosing to being close to a hanyō. Due to the unfair prejudice and hate half-demons receive on a daily basis, many of them sought to resolve their impurity by either becoming full demons to be stronger than their oppressors or full humans to be accepted by the peacefulness most humans live in. However some are just happy the way they are and accept their heritage without question such as Jinenji or eventually Inuyasha, for Kagome's sake.

Aging & Behavior
The half-demon aging process is difficult to figure, however there are guesses on how it work. The first is genetics which ever parent has more dominant genes will dictate the child's age rate. However another theory is that all half-demons start the aging as human until they his maturity or double digits (10yrs).

It is possible that some half-demons also have some attributes of their demonic side. When Inuyasha lay on the ground to take a smell, Kagome had the impression that he looked "like a dog". In a episode, she even throws a stick, so Inuyasha catches it, whereupon he is offended. Because Inuyasha is the only hanyō who is seen very often, but it is unknown whether other half-demons also show similar behaviors.

Powers & Abilities
While a hanyō can rarely be as strong as the demonic parent without becoming a full yōkai, most hanyō seem to be powerful enough to not only deal with any human hostilities, but also to easily dispatch most yōkai if their will and aggression is very strong. It seems that this attribute mostly applies to the demons strong enough that their hanyō spawn are more powerful than an ordinary Yōkai even when diluting their power with human blood. Inuyasha is the prime example of this, born of the Inu no Taishō, a very powerful daiyōkai.

A half-demon does not always possess the self-healing factor of a demon. Inuyasha is aged more than 200 years, only slowly, and can recover within mere hours or days from heavy injuries, even growing a new fang in half a day. However, Jinenji seems to grow old at human speed, and recovers from injuries at human speed. This could be because Inuyasha's demon genetics are more dominant and thus grants him longevity nearly equivalent to a demon while Jinenji's human genetics are perhaps more dominant which results in his human aging due to the difference in strength of their yōkai fathers. Though this could also be up to chance as the hanyō children of Hōrai Island are shown to still have the youthfulness of children despite having lived on the island for at least over 50 years and none of them have daiyōkai parents if the difference in their powers to Inuyasha are of indication.

In addition, many hanyō also have special powers that are rare or unique, depending on what kind of yōkai they are related to. Inuyasha has sharp claws and the attack "Sankon Tessō". Shiori can create powerful barriers. And Ai can supposed to have powers that are beneficial to her in the water. For a young child she swam in a surprisingly short time, a long distance from the Hōrai Island to the mainland.

Human
Half-demons have a big weakness. Once a month, they lose, for one day or one night, their demonic powers, and are no different from pure humans. Both Inuyasha and Kōga have said most half-demons hide the time of their weakness out of fear of being killed.

Demon
Vice-versa, a hanyō can also become a pure demon when he endures great pain or more commonly, their life is in danger. In this case, they are also as strong as the yōkai from which they are descended from. Inuyasha is the only hanyō we see in this form, and as a yōkai he is wild, cruel, and randomly kills, sometimes laughing as he does so. He takes great pleasure in killing, and cannot tell friend from foe, even attacking Kagome.

As Inuyasha in the only half-demon we see in this form during the series, it is unclear if all half-demons lose their human minds. Since all hanyō share a human transformation however, it can be assumed all share a demon form.

Known Hanyō
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By Birth

 * Inuyasha
 * Izumo
 * Jinenji
 * Shiori

Hōraijima Children

 * Ai
 * Asagi
 * Dai
 * Moegi
 * Roku
 * Shion

By Unnatural Means
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 * Naraku
 * Sara Asano
 * Tsubaki

Trivia

 * The term "Half-breed" is used as an offensive term for hanyō.
 * In the movie, InuYasha: Fire on the Mystic Island, there is a secret haven known as Hōrai Island where yōkai and humans lived together in peace, raising many hanyō offspring who were accepted by all.