The more he came across powerful enemies, the more he realized his need to become strong and protect the ones he cared about. Zenitsu's desire to protect Nezuko especially gave him courage and made him realize the strength he'd had all along.
When facing Kaigaku during the Infinity Castle arc, Zenitsu debuts his brand new exclusive Seventh Form to Thunder Breathing. With this, Zenitsu finally has more than one tool in his arsenal and has overcome his own personal doubts and fears. While Zenitsu's character arc is short, this is a fantastic ending to it.
During his time training, Zenitsu attempted to escape many times, only to be brought back by Jigoro. Zenitsu believed that he would die, either from the training or as a demon slayer. Still, Zenitsu grew in strength, even if he never noticed, and his relationship with his teacher developed as well.
Through sheer will and anger, Zenitsu was able to overcome his cowardice and stay awake in battle against demons, shown during his bout with Kaigaku and Muzan, especially in the fight with the latter in which he refused to give up and persisted despite being enervated and injured.
Zenitsu is an incredibly powerful Demon Slayer, but he's always in fear. His nerves calm down when he's asleep, so that's when he awakens his “powers”. MANGA SPOILER AHEAD!!!
Thunder Clap and Flash—Godspeed is the most powerful of Zenitsu's derivations of the Thunder Breathing first-form technique.
Zenitsu — Anxiety
To the surprise of absolutely nobody, Zenitsu is anxiety incarnate. He starts out the series so paralyzed by fear that he can't even fight when he's conscious, and so he's only able to fight when he's passed out.
His immense stamina and will, makes him a powerful opponent as he is able to go long periods of time in battle without giving up. Just like his comrade Tanjiro, Zenitsu also refuses to give up in the heat of a battle and was able to battle with extremely stronger demons such as Kaigaku and Muzan.
He was forced(not in a bad way) to train because his Master Jigoro Kuwajima saw potential in him, but despite of rigorous training He could not learn more than one form. He has only learned the first Form and has mastered it. Mastered it in a sense that he can use technique multiple times (six fold).
Kaigaku overpowering Zenitsu with his Blood Demon Art-enhanced techniques.
Tanjiro Is Strong, and Stronger than Zenitsu as he uses Sun Breathing.
2) Tanjiro Kamado
With Sun Breathing, which is regarded as the paramount of all Breathing Styles, Zenitsu will have a hard time subduing Tanjiro and will be defeated by the latter in no time.
Zenitsu is an incredibly powerful Demon Slayer, but he's always in fear. His nerves calm down when he's asleep, so that's when he awakens his “powers”. MANGA SPOILER AHEAD!!!
Though he's on a journey to get over his fears and wants to be a better version of himself. However, as every Demon Slayer affiliated with a Breathing Style develops certain forms which give them an advantage in combat, Zenitsu could only learn the first form of Thunder Breathing: Thunderclap and Flash.
Inosuke is probably the closest to Zenitsu in terms of power, considering they're both new Demon Slayer recruits and they're both less skilled than Tanjiro. If they ever were to face off, however, it's likely Inosuke would win.
Thunder Breathing is one such technique that Zenitsu has used to great effect in the series. Of course, Zenitsu is only the master of the first form, but it goes without saying that the other techniques of Thunder Breathing will also be awe-inspiring to witness in Demon Slayer.
During their fight, Zenitsu was at a major disadvantage against Kaigaku until he used the seventh form called “Honoikazuchi no Kami,” literally meaning “Flaming Thunder God.”
Unfortunately, he retired at the age of 35, when he lost his right leg in a fight with a demon. Since then, he devoted his time to teaching the next generation of demon slayers, most notably, Zenitsu Agatsuma, who lovingly called him "grandpa".
Zenitsu is clearly on the same level as Hashira. If we compare him to Shinobu, his speed is far better, while she lacks quite a lot in raw power. There is a good chance that he could beat Shinobu if the two decide to fight.
Superhuman Hearing: Zenitsu has always had enhanced hearing, being able to hear what others can't. He is able to hear a faint difference that is normally indetectable to humans in the sound of a moving human and a moving demon. His hearing gives him extra awareness for danger.
1) Tanjiro Kamado
Although he and Zenitsu along with Inosuke, started training together, he excelled both in the matters of strength and swordsmanship. Tanjiro with his Sun Breathing is more powerful than Zenitsu.
Zenitsu is an incredibly powerful Demon Slayer, but he's always in fear. His nerves calm down when he's asleep, so that's when he awakens his “powers”. MANGA SPOILER AHEAD!!! Zenitsu becomes a lot more courageous and stands up to a powerful demon while wide awake.
Unfortunately, the answer to this question would be, no, he did not. Zenitsu, along with Tanjiro and Inosuke got way stronger than average corps members with training. In fact, he became one of the very few to even invent a new form of Thunder Breathing. However, his dream of becoming a Hashira was never realized.
In the Naruto series, Zetsu, of the Akatsuki, has different identities. The two halves of Zetsu's body have distinct personalities but work together as a whole. In a pinch, he can switch between his White and Black Zetsu faces, located on either side of his face.