Shinjuro Rengoku struggled with alcoholism and bitterness after losing his wife, neglecting his sons and causing regret. Shinjuro had an inferiority complex about Flame Breathing compared to Sun ...

Rengoku and Tanjiro are connected through Flame and Sun Breathing; however, there is more to their relationship than echoes of the past.

Shinjoru Rengoku later reveals that the Hinokami Kagura is the legendary breathing style known as Sun Breathing. Tanjio realizes that using this style increases his overall power and speed.