Demon Slayer: Kimetsu No Yaiba’s most panic-stricken character out of the trio, Zenitsu Agatsuma, has a peculiar yet fascinating personality. He often claims that there is no tomorrow for him, because of the risk of uncertainty to life, that comes with the profession. Dealing with a constant state of anxiety, Zenitsu often tends to avoid vulnerable situations.
Note: This article contains spoilers!
Clearing the final selection, Zenitsu made it to the Demon Slayer Corps. The question of how he made it got unveiled later where he confronted Tanjiro Kamado: "I thought I'd die in the final selection but luckily I survived," meaning he spent the required seven days of qualification in hiding and did not engage in combat with demons.
Why Zenitsu Falls Asleep in Demon Slayer?
Zenitsu, while awake, is aware of his surroundings, and can sense demons quite efficiently with his 'Enhanced Sense of Hearing', but when it comes to even slight contact with a demon, he blacks out.
So, to sum it up, his fear of going against terrifying demons that could end his life, drives him to fall asleep. However, in an unconscious state, he becomes a totally different individual, who takes mere seconds to slay a demon and get the job done.
Despite his cowardice, Zenitsu wants to step up and live up to the expectations of others, especially Nezuko, because of his affection towards her. He unwillingly goes after Nezuko to Mount Natagumo, only because he was concerned that she might get hurt.
Even with such immense strength and speed, he has low self-esteem that makes him unable to withstand a demon. But when he's asleep, his alternate unconscious self wipes out the traces of demons like they never existed.
Being a Thunder Breathing user (one out of ten acclaimed Breathing Styles) and that too trained by Jigoro Kuwajima himself: a former Hashira, makes Zenitsu a skilled and potential Demon Slayer, who can surpass his limits. While unconscious, Zenitsu's combat is quite intriguing, as he amplified Thunderclap and Flash to sixfold, the only Thunder Breathing he can do.
Zenitsu is genuinely trying to better himself, as shown in the first episode of Entertainment District Arc where the trio goes through intense training for rehabilitation. Furthermore, in the third episode, Zenitsu displayed courage by confronting Daki(disguised as an oiran) knowing that she's an Upper Moon Demon, in order to save a little girl, but this time in a conscious state.