Yoriichi Tsugikuni (継つぎ国くに 縁より壱いち Tsugikuni
Yoriichi) is a major supporting character in Demon Slayer:
Kimetsu no Yaiba. He is a legendary Demon Slayer who lived
nearly 500 years ago during the Sengoku era (the Golden Age of
Demon Slayers), as well as the strongest Demon Slayer to have
ever existed. He is also the inventor of Breathing Styles, being
the one who created the first ever Breathing Style that would
eventually become the Hinokami Kagura used by Tanjiro Kamado and
members of the Kamado Family.
Yoriichi is the younger twin brother of Michikatsu Tsugikuni,
who later became a demon and joined the Twelve Kizuki.
Sakonji Urokodaki (鱗うろこ滝だき 左さ近こん次じ Urokodaki Sakonji) is a retired member of the Demon Slayer Corps, having held the position of the previous Water Hashira (水みず柱ばしら Mizu Bashira). He is the main cultivator of the Water Breathing style, having trained Makomo, Sabito, Giyu Tomioka, and Tanjiro Kamado.
Shinjuro Rengoku (煉れん獄ごく 槇しん寿じゅ郎ろう Rengoku Shinjurō) is the father of Kyojuro Rengoku and Senjuro Rengoku and the husband of Ruka Rengoku. He formerly served as the Flame Hashira (炎えん柱ばしら En Bashira?) of the Demon Slayer Corps.
Jigoro Kuwajima (桑くわ島じま 慈じ悟ご郎ろう Kuwajima Jigorō) is the man who trained Zenitsu Agatsuma and Kaigaku. He was formerly the Thunder Hashira (鳴なり柱ばしら Nari Bashira) in the Demon Slayer Corps