Kyojuro is the oldest son in his family of four; his father, mother Ruka Rengoku, and younger brother Senjuro Rengoku. His family has been a part of the Demon Slayer Corps for a long time, always producing Flame Pillars. His father was the former Flame Pillar but realised that nothing could beat the Sun Breath, the first and original breath, and despaired retiring from his duties. While his father was beating himself up over his incompetence, his mother died due to illness.