Tsukiguni Yoriichi

"The Swordsman of the First Breath." A demon slayer from the Sengoku period who used the Sun Breathing technique and laid the foundations for the current Demon Slayer Corps. Born with a flame-like mark from his forehead to his eyes, he had already entered the "Transparent World" at a very young age. He wore flower card-style earrings with a sun symbol. His Nichirin blade was jet black (much darker than Tanjirou's), turning bright red in battle. The sword's hilt was a four-lobe mokko shape, with a sharkskin grip and a black scabbard.

Despite his dazzling swordsmanship, his life was filled with hardship and misfortune. Born a twin in the Tsukiguni family, twins were considered ominous at the time due to inheritance disputes, and his birthmark made his father wary of him. After his mother protested, he was raised distinctly differently from his brother, Yoriichi, under the condition that he would enter a temple at the age of 10. Yoriichi, pitied by his brother Gankatsu, played and received handmade flutes from him when their father was not around. Not speaking until the age of seven, Gankatsu and their mother thought he was deaf. Gankatsu, aspiring to become the strongest samurai, deemed Yoriichi's ambition to be the second strongest unrealistic due to his attachment to their mother. However, when casually handed a bamboo sword by an instructor, Yoriichi knocked him unconscious with four strikes after being briefly instructed on the grip and stance, revealing his extraordinary talent. This talent, however, made Yoriichi feel a strong aversion to hitting others, and he no longer expressed a desire to become a samurai. After their mother's death, Yoriichi left home at the age of seven. His clinging to his mother's left side was actually to support her, as she was disabled on that side due to illness.

After running away, Yoriichi met a girl named Uta, who had lost her family to an epidemic, and they started living together in a mountain home. Ten years later, he married Uta, but while he was away to call a midwife for her delivery, demons killed Uta and their unborn child. Holding their bodies for ten days, he met a demon slayer, which led him to become one himself. He taught the breathing techniques to other swordsmakers, and with Gankatsu joining, they made significant progress until encountering Muzan Kibutsuji and Tamayo. The moment he met Muzan, Yoriichi realized he was born to defeat him, and during their battle, he completed the Sun Breathing forms upon discovering Muzan's multiple hearts and brains. He cornered Muzan without taking a fatal blow, but Muzan escaped due to a cunning plan. Failing to kill Muzan, letting Tamayo escape, and his brother turning into a demon and killing their lord led to demands for Yoriichi's seppuku, but the new lord stopped these demands, and Yoriichi was expelled from the Demon Slayer Corps.

Visiting the dilapidated house he shared with Uta, he saved Tanjirou Kamado and his heavily pregnant wife, Sumiyoshi, from a demon, becoming friends with the couple. He shared his life story with Tanjirou, expressing his remorse, but seeing their daughter Sumire's innocent smile reminded him of what he wanted to protect, bringing him to tears. As a parting gift, he showed Tanjirou the Sun Breathing forms and gave him his earrings. Despite the toll of his mark, he did not die young but met his brother, now the demon Kokushibo, 60 years later. Despite his unchanged sword skills, he prepared to face death but ultimately died of natural causes.

Highly skilled yet incredibly humble, Yoriichi lamented the lack of successors to his brother, optimistically suggesting that a new generation would soon emerge. He had a gentle nature, similar to his mother's, and was pleased when others were happy, a trait Uta could read beyond his expressions. He loved only Uta throughout his life and remained single after her death, leaving no direct descendants. He kept the flute given by his brother in a pouch made from Uta's kimono.

Sun Breathing

The original breathing technique, with forms named after the sun and flames, was the only one during the Sengoku period that could manifest a bright red blade that hindered demons' regenerative abilities. It was the basis for Tanjirou's Hinokami Kagura.

Thirteenth Form

The strongest technique Yoriichi completed during his fight with Muzan, executed in less than a moment, pushing Muzan to the brink of death.

Transparent World

A technique that allows one to see through an opponent, predicting their next move by observing their muscles and skeletal movements. Yoriichi had mastered this from an early age.