Uta

The Demon Slayer Mark grants enhanced abilities, but according to Brother Michikatsu, anyone with the mark will not live to be 25 years old.
Access to the "Transparent World" - allows you to see the muscles, blood flow, and joint movement of your opponents, accurately predicting and anticipating movements and attacks
Nichirin Sword Color Change - During battle, Yoriichi can optionally color his black sword bright red, allowing him to counter the enhanced regeneration of demons.
The creation of the "Breath of the Sun" - the primordial breath from which all other breaths originated.

The younger twin brother of Michikatsu Tsugikuni, who later became the demon Kokushibo.
He was born with a strange mark on his forehead - his father considered him cursed and wanted to kill him, but the baby's mother did not allow this.
Until the age of 7 he did not say a single word; he was considered deaf and dumb.
At the age of 7, he defeated his fencing instructor in 4 moves after seeing them for the first time.

Appearance: A tall, handsome man with a fire-shaped mark on his forehead and long, spiky black hair with red tips tied into a ponytail, 190 cm tall, wears a light brown yukata, a black hakama, a red haori, white socks, and a white zori with red straps.

Lack of emotion. Kokushibo described Yoriichi as a person who never showed emotion. However, in old age, upon seeing his older brother, Yoriichi cried, likely out of pity.
Determination to defeat demons. Yoriichi firmly believed that the world was beautiful, but corrupted by the existence of demons, and he was determined to defeat them all, especially their king, Muzan Kibutsuji.
Guilt. When Yoriichi failed, his sense of honor caused him to experience a strong sense of guilt, and he began to consider himself worthless.

Initially, Uta was a very quiet and lonely girl due to the loss of her entire family at a young age. She was sensitive and compassionate, for example, bringing home tadpoles and, after caring for them, deciding to return them to their parents. When meeting Yoriichi, she was constantly embarrassed and was glad he chose her.

A pale-skinned girl with large eyes, long eyelashes, and small, wide eyebrows. She had straight, dark hair just below her shoulders, tied in a loose ponytail with a ribbon, and three pairs of short strands on either side of her face. She wore an orange kimono with a dark green geometric pattern, over which she tied a white apron. She was 177 cm tall.