9/10 Zenitsu Agatsuma Swiftly Defeated Kaigaku With A New Technique. Kaigaku was originally a disciple of Jigoro Kuwajima along with Zenitsu.
Zenitsu Agatsuma vs Kaigaku is a battle that took place in the Infinity Castle. It focuses on the battle between Zenitsu Agatsuma against Upper Rank Six Kaigaku.
Fortunately, Zenitsu was able to single handedly beat the Upper Moon 6. Not only did he defeat the demon, he also created a seventh form called the Flaming Thunder God. These are the demons who have been given the title of Upper Moon 6 in Demon Slayer.
Infinity Castle Arc
Kaigaku is ultimately beheaded by Zenitsu's Honoikazuchi no Kami technique.
After the deaths of Daki and Gyutaro, Kaigaku was promoted to become Upper Moon Six of the Twelve Demon Moons due to his power and confronted Zenitsu as a rematch he always desired.
10) Zenitsu
He certainly has speed and was able to keep up with Daki during the Entertainment District arc. While some might say that he could one-shot the Upper Moon demon Kaigaku, the demon was nowhere near the level of an Upper Moon since he was not used to his powers.
Tanjiro decapitates Akaza with the Hinokami Kagura: Setting Sun Transformation. Akaza was bewildered, wondering how Tanjiro did not have any fighting spirit, comparing this feeling to fighting against a plant. He acknowledges that Tanjiro surpassed his speed.
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.
1/7 Seventh Form: Honoikazuchi No Kami
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.
Yoriichi was born with the Demon Slayer mark and prowess in swordsmanship. His powers were beyond comparison as he defeated Muzan once and had him on the verge of death until he managed to escape.
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.
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.
Many who are weak will not survive, but by finding the courage and strength within himself, Zenitsu was able to become stronger than most.
Overall, Zenitsu is an extraordinary powerful Demon Slayer capable of singlehandedly bringing down an Upper Rank, which said to be able to overpower 5 Hashira, in 10 minutes, albeit he would have beheaded Kaigaku in a heartbeat if it wasn't for his feelings of melancholy and pity.
Yes, he faced one of the requirements to become one!!! He defeated on of the 12 Kizukis by himself and is at the rank of Kinoe! But, of course, the Demons Slayer Corps disbanded, so I guess he doesn't have a chance to be one, but either way I'd say yes!
He is a Demon Slayer in the Demon Slayer Corps, a member of Team Butterfly as one of it`s founding members, and the Captain of The Time Travelers; he has replaced this world`s Kaigaku and is Zenitsu Agatsuma`s older brother who supposly died protecting some of his fellow Demon Slayers from harm.
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 always performs a single form because that is the only form he knows. His attack always start with this positioning, and end result is this way.
Exploring Zenitsu's fighting abilities in Demon Slayer
Zenitsu has perfected the first form only and is seen performing it only when he's unconscious. But the manga shows that he can fight without fainting or going unconscious.
The spider demon explains that the spider that bit Zenitsu earlier was one of his, and Zenitsu has been poisoned and will slowly start turning into a spider. As always, Zenitsu goes into a state of frenzy, and then he climbs a nearby tree.
Inosuke always displayed raw strength and courage from the first few chapters of Demon Slayer. One might even argue that he was far stronger than Zenitsu during the first arc.
13/15 Zenitsu Agatsuma Defeated An Upper Moon On His Own
He falls asleep when he crumbles under the weight of his own fear, and his body fights on instinct alone, utilizing his Thunder Breathing Style. He proved that he can be a capable fighter even while awake, defeating Upper Moon 6 on his own.
After various battles within the Dimensional Infinity Fortress the remaining Upper Moons are killed by the hands of various Demon Slayers. The last member, Upper Moon Four Nakime, ends up being killed by Muzan Kibutsuji himself to stop the Dimensional Infinity Fortress from being controlled by his enemies.
While Mist Breathing has six forms, he created a Seventh Form: Obscuring Clouds during the fight with an Upper Rank Demon. Muichiro can defeat Akaza easily with his petite body that leverages his speed. Moreover, his ability of Transparent World can aid him in landing a fatal blow on Akaza's weak spot.