Yoriichi Tsugikuni died of old age while standing during a combat against his demon-turned brother Michikatsu, also known as Kokushibo. Although he almost killed Kokushibo by slitting his throat, Yoriichi succumbed to old age and exhaustion before he could deliver the finishing blow. He lived well into his 80s despite the Demon Slayer Mark typically causing death by age 25. Yoriichi thus died an undefeated warrior, passing away standing on his feet before killing his brother.