Transformation

is an ability to change one's physical appearance. It was a common ability among many yōkai. Some yōkai were able to hide their true appearance by taking on a humanoid form. Examples include Sesshōmaru, his mother, and Tōga. Other yōkai were capable of disguising themselves as another individual. Examples include Shippō, Hachiemon, and Naraku. Those who were in possession of the Shikon no Tama were also able to change their appearance to a more menacing form. This includes Mistress Centipede, Shibugarasu, and Naraku.

Half-Demons
Many half-demons have the capacity to shift from their base forms to either full human or more demonic. Although, they mostly are triggered under certain conditions.

Human states
Inuyasha, Jinenji, Towa and Shiori lose their demonic powers at certain times when they turn human. During these times, their appearance would resemble more of a regular human with darker colored hair, natural eye colors and lack of demonic features and abilities.
 * For Inuyasha and Towa, this occurs during the night of the new moon.
 * For Jinenji, this occurs one day a month.
 * For Shiori, this occurs during a solar eclipse.

Demonic states
Whenever a half-demon is placed into a situation where their life is in danger, their demonic nature would awaken to protect its host. As mentioned by Bokusenō, the demonic blood would consume the soul of the host, making them a dangerous beast who cannot differ ally from enemy. So far, only those descended from the Great Dog Demon's bloodline have been shown in this state.

Object states
Some of those weapons can change. Verwandlung 變身
 * As Towa holds the Hoshikiri no Fue change into Zanseiken and back.