NOTE: I calculate demon years by aging 1 human year every 10 years. This means that a demon who is 7 years old in human years is really 70 years old in demon years.
Another Note: I don't leave a lot of things out so there might be some spoilers to the series or movies that will not be marked, you are reading these at your own risk.
Species: Dog Demon
Age: 19 (190 in demon years)
Family: Inunotaisho (father, deceased), mother (not mentioned), Inuyasha (half-brother)
Likes: Fighting honorable and worthy battles, Rin
Dislikes: Naraku, all humans except Rin, Inuyasha
Weapons: Tenseiga, Tokijin, and claws
Sesshomaru is Inuyasha's older half-brother (same dad, different mother). As a full demon he is much stronger than Inuyasha and a lot more graceful. He kills with precision and perfection and does not hesitate for anything.
His father, whom he is extremely proud of for his power and position, left him one of the two swords he had made from his own fang, the Tenseiga which could heal 100 souls in one swing. Sesshomaru was disgusted by this because he had no use for the sword and desired Tetsusaiga, the sword left to Inuyasha.
He detests humans but he saved one human girl who had taken care of him after an injury from Inuyasha. The girl was Rin, who had been killed by wolf demons when they raided her village and killed her family. Sesshomaru used the Tenseiga for the first time to revive her and now she follows him everywhere along with Jaken, his servant.
Rin is almost like an adoptive daughter for him as he treats her, in his own way, respectively while detesting other humans.
Species: Half-Demon(Demon later on)
Age: 23 (230 in demon years)
Likes: The Sacred Jewel, Kikyo, destroying anyone in his way
Dislikes: When Kagura tries to betray him, Inuyasha, and just about everything
Weapons: Sword (when human), miasma
Naraku is the main villain, the one that almost everybody has a bone to pick with. Like Inuyasha, he is a half-demon although he was not born this way. He is the product of the paralyzed bandit, Onigumo after he sold his body to a horde of demons. As such, Naraku's body is composed of many different demons. He is capable of choosing the night he becomes vulnerable, unlike Inuyasha, which helps him reorganize the various demons within his body to make himself stronger.
He is completely ruthless and does not care what happens to others, so long as he gets what he desires. He loves nothing more than to toy with people's hearts and command their loyalty.
Unlike some demons, he does not go out of his palace to fight a lot, instead he sends puppet copies of himself or his incarnations to do his bidding.