Zenitsu has short, blonde hair, which was originally black and brown eyes with thick eyebrows. He wears the standard Demon Hunter uniform, along with a yellow Haori with a white triangle pattern on top.
Zenitsu is a coward and is constantly claiming he doesn't have long to live due to the dangerous job of being a Demon Hunter. He is also a bit of a womanizer and likes to hit on girls who he thinks are cute and ask them to marry him -- much to their annoyance.
Zenitsu has low self-esteem but still wanted to live up to the expectations others set up for him, but he was constantly afraid and would always cry and run away. He claims he wants to live a modest life where he can be useful to someone.
(Source: Kimetsu no Yaiba Wiki)