The reason for this is pretty simple. Zenitsu wasn't able to master the other 5 forms. He never wanted to learn any breathing techniques. or fighting techniques, nor he wanted to join the Demon Slayer Corps. He was forced, not in a bad way, to train because his master, Jigger Okuwajima, saw potential in him.
With his master gone, Zenitsu can no longer learn the remaining five forms. Therefore, during his fight with Kaigaku, an Upper Moon Six, he created a 7th form.
His second form is no exception, with Rice Spirit being a succession of five slashes that are accompanied by his black lightning. It's fatal to most opponents, although Zenitsu had the constitution and awareness required to avoid any major damage from this attack.
The reason for this is pretty simple, Zenitsu wasn't able to master the other 5 forms. Since he could only use the first form he decided to master it and came up with extensions like Thunder clap and flash six fold.
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.
Thunder Clap and Flash—Godspeed is the most powerful of Zenitsu's derivations of the Thunder Breathing first-form technique.
Demon Slayers are known for their strength and bravery in battle, but not Zenitsu. Despite his cowardice, he's one of the strongest in the series.
Why Zenitsu could not become a Hashira in Demon Slayer. Fans have wondered whether Zenitsu ever got to realize his dream of becoming a Hashira at all. 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.
Zenitsu was even able to exert himself for around half an hour during the fight against Muzan, even being able to surpass his limit of only being able to use his Thunderclap and Flash: Godspeed technique twice a day before his legs gave out.
To sum it up, it is possible for Zenitsu to fight without fainting and it has been shown clearly in the manga. While he only perfected the first form, he trained hard enough to create a new form that didn't exist before.
As we've seen multiple times, Zenitsu is only able to use Thunder Clap in flash. even though Thunder Breathing has 6 forms. The reason for this is pretty simple. Zenitsu wasn't able to master the other 5 forms.
The eccentric and flamboyant Tengen Uzui is the current Sound Hashira. This Breathing Technique gives him echolocation and other advanced hearing abilities.
Tanjiro isn't Faster Than Zenitsu, not at all. He is Strong but Slow. So, Zenitsu Will Probably Chop Him Down to bits before tanjiro even pulls out his sword properly.
Breath of the Sun
It's the oldest and most powerful breathing style that was used to develop the Flame, Water, Moon, Thunder, Stone, and Wind Breathing techniques that demon slayers use to this day. It mimics the intensity and versatility of the sun, lessening a demon's ability to regenerate.
172.1 Km/h Whenever he performs his thunderclap And flash move.
Shinobu Kocho is a capable Demon Slayer whose worthy of being the Insect Hashira. That being said, she's arguably the weakest Hashira when it comes to pure strength.
But, comparing the two characters in their best forms, Zenitsu might be just a tad bit faster owing to his Godspeed move.
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.
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.
While awake, his nerves and fear cause him to freeze up so he cannot move. When his life is in danger, his nerves and fear grow so strong that he passes out. But while asleep, his nerves are no longer holding him back, allowing him to fight and move with great judgement, precision and skill.
Thirteenth Form of Sun Breathing in Demon Slayer
It involves a combination of all existing Sun breathing techniques — but performed in a consecutive manner. This technique's primary purpose is to slash all the twelve vital organs of a demon. Each form targets a specific organ. Tanjiro only used it once in the manga.
The Thirteenth Form of the Sun Breathing Style is unique in the sense that it doesn't really have a name of its own. Rather, it's a combination of all the twelve forms present in this style, used in succession to maximize their power. This move was devised by Tanjiro solely to defeat Muzan.