Shinjuro Rengoku

Shinjuro looks a lot like his sons, Kejuro Rengoku and Senjuro Rengoku, he has unruly orange hair that frames his face, turning red at the ends above his ears, which he casually ties back at the back of his head. He has fair skin, bushy black eyebrows and bright orange eyes that turn red near the pupils, which are slanted inwards and shaped in such a way as to give him a ferocious appearance.
Shinjuro wears a traditional kimono. When he was a Fire Hashira, he also wore a haori with flame-like combs on the end, which Kejuro wore when he was a Fire Hashira. In the arch of Infinity Castle, he is shown with a katana with a fire guard similar to Kejuro, with what appears to be a flame pattern on the scabbard.

Shinjuro is a very short-tempered man, especially when it comes to the Demon Slayer Corps and his son Kejuro, the mention of which infuriates him. He seems to be behaving offensively, rudely insulting the recently deceased Kejuro and knocking Senjuro to the ground during his fight with Tanjiro. He is also an alcoholic - his first action after waking up after being knocked out by Tanjiro is to buy alcohol, and he is often seen drinking with sake.
Shinjuro feels a sense of inferiority that arose after reading The Chronicles of Hashira's Past Flame, where Solar Breathing is described as the original and most powerful breathing style. He ridiculed other styles, calling them "cheap imitations" of the Sun's Breath, and accused Tanjiro of coming to their house to ridicule them for their superiority after recognizing his hanafuda earrings.

It is not known why, but Shinjuro hates animals.