i know rengoku is sort of generally seen as the man who took tanjiro, inosuke and zenitsu under his wing, but i think it was with tanjiro that rengoku truly took on the role of a teacher. inosuke, on the other hand, is cared for mostly by shinobu.

it is with her he makes his promise. it is with her tsugoku that he avenges her death. it is with her that he forgives his own weakness so that he might grow stronger. and while rengoku did serve as an inspiration for the trio during the train arc, this must change of course.

zenitsu, perhaps whether he likes it or not, is undeniably influenced by uzui and arguably ends the red light district arc really looking up to him. though this might not have been the case from the start, uzui becomes a role model to him of sorts. rengoku's replacement.

tanjiro, too, is forced to move onwards and finally finds a strange, comforting sort of advice in the other pillars, but gyomei's training seems to mean the most to him. the idea of endurance resonates with tanjiro. he knows pain as deeply as himejima does. it only makes sense.

and while rengoku has undoubtedly touched the lives of the trio in a way that was much too shortlived, he also opened the path for them to find other mentors, learn from them, stand on their own two feet, and therefore become independent. they grow, thanks to him.