Haori | Demon Slayer: Kimetsu no Yaiba | Agamatsu Zenitsu

Zenitsu wears a paler brown version of the standard Demon Slayer uniform, which consists of a dark brown button-up jacket, a white belt around his waist, and tattsuke hakama pants that extend, as well as his signature white-triangle-patterned, yellow-and-orange gradient haori. 

The pattern on Zenitsu's haori may be inspired by Uroko, a traditional Japanese pattern that symbolizes scales. Samurai would wear clothing with this pattern to protect themselves from harm.

Demon Slayer: Kimetsu no Yaiba 
In Taisho-era Japan, Tanjiro Kamado is a kindhearted boy who makes a living selling charcoal. However, his peaceful life is shattered when a Demon slaughters his entire family. His little sister Nezuko is the only survivor, but she has been transformed into a Demon herself! Tanjiro sets out on a dangerous journey to find a way to return his sister to normal and destroy the Demon who ruined his life.

Zenitsu Agatsuma  is one of the main characters of Demon Slayer: Kimetsu no Yaiba and along with Inosuke Hashibira, a travelling companion of Tanjiro Kamado and Nezuko Kamado. He is also a Demon Slayer in the Demon Slayer Corps.

(from Kimetsu no Yaiba Wiki)