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.
This mastery allowed Zenitsu to form a Seventh Form of Thunder Breathing that is unique only to him: Honoikazuchi no Kami. While this move might seem similar to Thunder Breathing's First Form, the speed and power of this technique are on a whole new level.
Zenitsu creates his own form called Seventh Form: Honoikazuchi Nokami. Through this form, he is able to conjure a creature akin to a dragon that breathes thunder and fire. When combined with God Speed, his power and strength increase, giving him the ability to defeat demons like Kaiju, from the Upper Moon Six.
Adding that to the fact that he knew the First Form, which was the basis for all the other forms, we can conclude that Zenitsu really could learn all the other forms.
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.
So in a nutshell, Zenitsu wasn't able to master the other five forms, but later in the Infinity Castle Arc, during the battle with Kaigaku, Upper-Rank Six Demon, he created a Seventh Form: Flaming Thunder God.
Zenitsu is definitely faster but Tanjirou is more tactical and more versatile. Tanjirou could lose if he has no idea what Zenitsu can do, but if he does he can easily anticipate. Currently in the manga, Tanjirou is definitely stronger.
While unconscious, Zenitsu is a force to be reckoned with, but his actual power is discovered when he is awake. While awake, Zenitsu was able to match the upper rank six, Kaigaku. He was also able to keep up with the Demon King, though he was in a weakened state during this battle.
Zenitsu trained under the former Thunder Hashira, Jigoro Kuwajima. Under Jigoro's strict training, Zenitsu only mastered the first form of Thunder Breathing.
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.
12 Water Breathing: Seventh Form – Drop Ripple Thrust
In order to counter these fast-moving balls, Tanjiro's first move was to use the Drop Ripple Thrust. This form involves a swift stab at a target and was used to reduce the impact of an oncoming temari. It is also known to be Tanjiro's fastest thrusting technique.
Thunder Clap and Flash—Godspeed is the most powerful of Zenitsu's derivations of the Thunder Breathing first-form technique.
However, in the manga, his original Seventh Form allowed him to overpower his former senpai. As such, right now, Zenitsu isn't the fastest character in the anime.
Nezuko marries Zenitsu Agatsuma in the Demon Slayer series.
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 Agatsuma is a part of the Demon Slayer Corps who the previous Thunder Hashira trained. Zenitsu is a skilled and able member of the organization but gets easily scared when facing demons. But as the series continues, we watch him grow as he eventually overcomes his fear of demons and fights them head-on.
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.
Tanjiro Is Strong, and Stronger than Zenitsu as he uses Sun Breathing.
Yoriichi Tsugikuni is the creator of the Sun Breathing style and is also the strongest demon slayer that has ever lived. He existed nearly 500 years prior to the events of Demon Slayer and struck fear into the hearts of every demon he came across.
But, comparing the two characters in their best forms, Zenitsu might be just a tad bit faster owing to his Godspeed move.
As the young slayer aids in picking off more and more of the Twelve Kizuki, Muzan finds just as many reasons to be scared of Tanjiro Kamado. Tanjiro also ends up being the one to land the final blow on Muzan's original body, further proving why Muzan is scared of Tanjiro throughout the series.
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".
172.1 Km/h Whenever he performs his thunderclap And flash move.