Taichi's father

 is the character that took care of Kohaku's wounds from a hound possessed by a Hitōkon. He first appears in Chapter 359 in the manga and Episode 1 in The Final Act.

During the story
While Kohaku tries to go after the Hitōkon who is hidden from sight, he hears a noise that he assumes to be the yōkai, but finds out it is a boy named Taichi. When his father comes over to see what was troubling him, he sees Kohaku and brings him into his home to treat Kohaku's wound on his arm. He even offers to stay overnight in which he accepts. During the night, Taichi goes out to pee when the Hitōkon possesses him and tries to attack Kohaku. When Taichi's father sees somethings wrong with him he goes near to help him only to get cut by him on his arm. Inuyasha and his group who are following after Kohaku came upon them spotting Kohaku in which they think he is killing Taichi when in reality he was trying to get rid of the Hitōkon. As the possessed child takes off to escape Kohaku, Inuyasha, and Sango, Taichi's father begs them to save his child. In the end, the Hitōkon was forced out of Taichi's body and Inuyasha returns the boy back to his father.

Manga vs. Anime
There are several scenes present in the anime that were not in the manga.
 * Taichi's father never asked Kohaku to stay overnight.
 * Taichi's father was cut in the arm at daytime immediately after he healed Kohaku's wound.
 * Taichi's father never had any interaction with Inuyasha and his group.