Given how talented Tanjiro is, it's likely he'd defeat Zenitsu, even if the latter could fall asleep and call on his powers. Tanjiro's demonstrated his ability to take down more powerful demons and adapt to training on more than one occasion, so it just makes sense.
Tanjiro Is Strong, and Stronger than Zenitsu as he uses Sun Breathing.
Abilities And Techniques
In the beginning of the series, Zenitsu is seen as a weak person who doesn't seem capable of much until he is asleep. In his sleeping state he awakens an extraordinary power that makes him an extremely powerful and skilled swordsman.
Although Inosuke possesses immense strength and endurance, he's no match for Zenitsu's insane speed and his Thunder 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.
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. The life of a demon slayer is one of hardship.
If he could, Rengoku would win simply because Zenitsu cannot perform Godspeed more than twice. Since Zenitsu only knows the first form, Rengoku would know what to expect and accordingly counter his moves, taking him down in the end.
Thunder Clap and Flash—Godspeed is the most powerful of Zenitsu's derivations of the Thunder Breathing first-form technique.
After Muzan was defeated, all the demons he created also perished immediately, so there was no point of a Demon Slayer corps anymore. As a result, Zenitsu did not get to become a Hashira even after becoming strong enough to bie one. Demon Slayer is one of the most popular anime series going on right now.
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.
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.
why tanjiro's head is so hard? Well, it's thanks to his genetics, as his mother, Ki Kamado, passed down the trait of a rock hard head to him. In fact, Nezuko heard a story about their mother. scaring away a boar by headbutting it, which shows that Ki was also very tough and fearless.
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.
Among the current generation members, Shinobu and Zenitsu are the fastest characters in the series. According to the Upper Moon 2, Shinobu was the fastest opponent he had faced and was unable to react to her attacks due to its speed.
Sun Breathing has the second highest number of known techniques of all the breathing styles. It has twelve forms that can all be combined into an extremely powerful thirteenth form. It is second only to Moon Breathing which has sixteen techniques, employed by the Upper Rank One demon Kokushibo.
Hinokami Kagura, also known as Sun Breathing, is easily one of the strongest Breathing Styles in the series by a wide margin.
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.
1. Gyomei Himejima. Gyomei Himejima, the Stone Hashira, is the strongest Hashira in the Demon Slayer corps in terms of strength and swordsmanship. He is the only person who uses spiked flails and an axe instead of standard swords to kill demons.
There are six forms, but Zenitsu could only learn the first form said to be the basis for the others yet he honed it to where he could fight against several strong demons. He later created a seventh form and defeated his former senior who had become the Upper Rank Six of the Twelve Kizuki.
NO. It's his subconscious mind that helps him fight. When he fainted out, his subconscious mind takes over( something like semi-hypnotic state) and unleashes the lighting breathing. Consciously he is not confident enough.
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.
Kaigaku realizes that Zenitsu is much more versatile and skilled with his swordsmanship than before. However, he still believes that no matter how much Zenitsu trains, he can never defeat an Upper Rank like him.
How fast is Zenitsu?? I mean it's difficult to tell, but at least 750 mph since he can break the sound barrier.
Inosuke even manages to keep up with Zenitsu's God Speed ability when he helps him behead Daki, although Zenitsu's speed was waning a bit at that point and they were coming in from different angles. But there's no getting around it, Zenitsu is faster.