1) Inosuke Hashibira Although Inosuke possesses immense strength and endurance, he's no match for Zenitsu's insane speed and his Thunder Breathing.
At this point Zenitsu has manifested his speed and power, and he was also able to keep up with the Demon King, Muzan, even when weakened. It's possible to say that his power easily matched the strength of a Hashira.
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.
3) Zenitsu Agatsuma
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.
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.
slow ?! , Deku was able to dodge and hit in a split second. And yet he is clearly faster than Zenitsu .
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.
But, comparing the two characters in their best forms, Zenitsu might be just a tad bit faster owing to his Godspeed move.
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.
Thunder Clap and Flash—Godspeed is the most powerful of Zenitsu's derivations of the Thunder Breathing first-form technique.
Zenitsu trained under the former Thunder Hashira, Jigoro Kuwajima. Under Jigoro's strict training, Zenitsu only mastered the first form of Thunder Breathing.
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.
The eccentric and flamboyant Tengen Uzui is the current Sound Hashira. This Breathing Technique gives him echolocation and other advanced hearing abilities.
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. Such a weapon takes immense precision and soundness to use without inflicting personal damage.
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.
Tanjiro would win, because Deku have no way of killing Tanjiro. Deku may be stronger but in the end Tanjiro would win by stamina or landing a hit at Deku, which have poison that would kill Deku.
In the last episode of the anime, we see both Zenitsu and Tengen moving very fast and cutting things in a flash. Supposedly Tengen is faster than Zenitsu, but there are some posts around saying once Zenitsu masters form #7 in the manga, he becomes the fastest demon slayer.
However, in front of Giyu, Zenitsu is a much inferior opponent. He is just a newbie, while Giyu possesses greater strength, immense speed, and superior combat experience. If Giyu fights Zenitsu, the latter will lose miserably.
Going beyond this, Giyu is one of the most combat proficient Demon Slayers seen throughout the entire series. Furthermore, his strength and abilities are always portrayed as seemingly a cut above the rest of the Hashira, solidifying his expected victory against Tanjiro.
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.
1) Shinobu Kocho
The Insect Pillar of Demon Slayer Corps, Shinobu is undeniably the smartest individual.
Hinokami Kagura, also known as Sun Breathing, is easily one of the strongest Breathing Styles in the series by a wide margin. It's the Breathing Style that served as the base for every other style in the series, which is no mean feat.
Yoriichi Tsugikuni is the strongest demon slayer character to have ever existed in the series. He is also the only person that Muzan was ever afraid of.
Zenitsu is scared of Kaigaku. Because he realizes that he, in fact, is a character made up in the mind of a real person. Therefore, he is having a mental breakdown.