Senjuro Rengoku

Rengoku Senjuro is the younger brother of Kyojuro Rengoku and son of Shinjuro Rengoku and Ruka.

Demon Train arc
Senjuro first appears in Kyoujuro's dream, asking if their father was happy to hear the news of Kyoujuro's inauguration as the Flame Pillar but was met with a different response and was saddened to hear the hopelessness of their father's mental situation.

Kyojuro later gave him words of encouragement and reassured him that things were not as bad as they seem and to do his best throughout life.

Red Light District Arc
Senjuro appears once again after the battle with Lower Moon One Demon Enmu and Upper Moon Three Demon Akaza and is seen outside of his some, presumably sweeping the entrance with a saddened expression.