"Oh, Zenitsu is such a coward lmao"
WRONG!!!! HE SUFFERS FROM DEATH PARANOIA!!!
When we first see him in Kimetsu, he does look like your steriotypical anime trope coward, but if you actually stop to think about it, he seems much more worried about being killed in general, that he is of other things, such as being betrayed.
On his first dialogue with a girl he's trying to pursue in the middle of a road, we see Zenitsu say that he needs her to marry him, because he's "going to die" as if he's already accepted it as a fact, something he's unable to change or stop from happening, Zenitsu is certain that he is going to die, and soon.
He fears oni's, of course, but in my interpretation, he does'nt fear them just BECAUSE they are oni's, but because he feels that he's weak, so weak in fact, that he's certainly going to be devoured by a oni, in his mind, there's not a scenario in which he's possibly going to survive, he's dead. If not on this mission, on the next one, and if not, then in another random mission.
When we see him beg for a bride or fiancee, he's in reality, just desperate to live his life to the fullest, since in Zenitsu mind, he's going to die young, when you think about it, it's pretty sad, we see Zenitsu say to Tanjiro that taking that girl away from him meant that he's going to die alone, and looking at Zenitsu's perspective, i can definitely understand his despair!
Zenitsu feels POWERLESS. he's scared of oni's because they represent certain death to him, and a death he feels like he cannot stop or control, he would feel the same if any other concept threatened his life, he judges himself too harshy, and due to his harsh judgment, considers himself too weak to fight back or defend his life.
Zenitsu is not your typical perverted anime boy, while he does annoy girls by asking them to marry him, i believe he isn't actively trying to harass them, but rather, he's just afraid of dying without living to the fullest and without someone by his side, he's just a teenage boy that wants love!
And the worst part: Zenitsu isn't entirely mindlessly paranoid in his worries and fear! The Hashira world is tough, we saw children stronger than him DIE on the final exam, like Sabito, for example! His worries and paranoia about dying aren't entirely irrational, he's actually pretty conscious of the world he lives in, compared to other slayers that act careless! Zenitsu is always trying to be careful! Of course, using other people as a shield is not a very morally good way of protecting yourself, but he does it on impulse because he's scared!
Now, how does that compare to someone who actually suffers with death paranoia?
Zenitsu is extremely paranoid of dying, treats it as a unchangeable fact, even when he's not in danger, he believes that he is, he's paranoid of being killed by the people around him, so Zenitsu is suspicious about them (like the old woman that gave shelter to hashiras) He consideres himself weak or unable to stop his own predestined death.
Those are all traces of someone who suffers with death paranoia, and i say that as someone that suffers daily with all sorts of episodes, thinking someone close to me is going to kill me, thinking I'll die randomly, feeling unable to stop what i feel is certain, those are all things i feel daily, and that's why i felt the need to do this dissertation, i think the fandom overlooks his mental health issues, but that's just my interpretation of him, as a beginner Kimetsu no Yaiba fan, im super excited to see him grow and get more comfortable with being a hashira, as well as understanding he IS strong!
Thank you for reading :)