Story of "Breath of Thunder" :- The glory of Zenitsu

Chapter oneshot

"It's all right to cry, it's all right to run away. Just don't even give up"

Jigoro Kuwajima

This is the line which make the character named "Agatsuma Zenitsu"from demon slayer.

Unlike Tanjiro and Nezuko, who have been living with their family for over than 10 years, he started with nothing. He was abandoned as a child, considering Inosuke, the jungle boy is lucky enough to at least have a blanket with his name on it, which what he doesn't have.

That's why, he always want to create his family, later on, the girl he loved ran away with another guy, putting a mount of debt on him. But at last, he was saved by a strict but gentle old man, Jigoro Kuwajima, the former Thunder Hashira and the strongest Hashira of his time. Thus, his title was "Roaring Hashira".

Our girl crazy started training with his foster "Gramps" eldest disciple, but only was able learn the first form within his one year of training, which is also known as the foundation of Thunder Breathing, hence the easiest one.

That's why the older disciple started to belittling him, saying that their sensei is an amazing person, yet he's wasting time after training him. Thus this is one of the reason why he always fears of death and demons.

But their master sensed a potential inside him. Not to mention, the Hashira-level Thunder breath user have a enhanced sense of hearing. So he told him to practice the first form and cross it's limit.

But he couldn't take it anymore. He tried to escape from the training, but all was in vain. So he once climbed up the tree, but then a lightning strikes on the tree, making his black hair blond. Maybe it's a signal from the thunder god Raijin that he is meant for what his master chooses him for.

But the fact that he can perform only the first form always keep him frightening. So  his fighting ability during his unconsciousness is sure because of the fear which got developed inside him. Now someone gonna say, "This make no sense" but since he can hear people's talk and thoughts during his sleep, it kinda make sense. His hearing also can detect danger, and difference between a human and demon, and even help to know how nice the person is.

Now, practicing that single form again and again, he was able to creat augments to improve his first form. They are 'sixfold', 'eightfold' and 'godspeed'. And for this his first form become the strongest first form among the Thunder Breath user.

'Sixfold' and 'eightfold' is for repeat the same Thunderclap and Flash move as the number of folds since the first form is only consists of a single dash and slash. Using sixfold', he was the only one in the trio who was able defeat a demon alone in Mount natagumo, without breaking his sword.

The technique 'godspeed' help him to dash so fast that with his Thunderclap and Flash that even Upper Moon 6, Daki can't react to his move, although she shares 50% of her power with her brother. But he can use this technique twice a day, and his legs become useless after using it for the second time.

But the peak of his character arc, also known as one of his beat fight took place in the dimensional infinity fortress, where he met his senpai, who is now a demon.

This demon, known as Kaigaku, occupied the place of upper moon 6 in no time. Most of the fans say that he barely make the place as the lower moon were disbanded, but this isn't actually true. Inside the fortress, every demon (except UMs) were designed as lower moons, and most of them are way more experienced than him. This shows that without any experience, he ate a lot of people to make the rank. I can bet, if he lived for a year or two, he might able to replace Douma, UM 2.
But this time, Zenitsu didn't get unconscious. Instead he started to roast this demon, phrasing him as the empty slot filler of the lowest rank.

But the roasting voice suddenly changed into a loud but soft cry, asking why a person like Kaigaku, who was passionate about learning Thunder Breathing, the true Tsuguko of thunder Breath, became a demon. Because of this, their sensei committed seppuku as an atonement. And his death was a slow one, as nobody was left to cut his head while he slit open his stomach with his blade because Zenitsu was away at that time, Kaigaku became a demon and ate the rest of the students.

But this demon was something different! He thinks their Sensei is senile as he wanted to make him and Zenitsu as his joint Tsuguko, he actually dissatisfied from the fact to being compared with a crybaby who can do only the first form, thus he choose the path to became a demon due to his unfortunate encounter with Kokushibo, UM 1, who turned him into a demon, to live long and take revenge from Zenitsu

Now, Kaigaku used all the the known Thunder Breathing forms, except the first one in order to kill Zenitsu. But even he was looking strong and determined to kill him, was suffering from the shock that the one he look upon upon is a demon by himself now. He took all the attacks because he was taken aback from the fact that his so called 'aniki' is now fighting against him as a demon. The attack is now stronger with blood demon arts, and it started to burn his flesh and crack his skin, and he started to bleed from the cracks on his body. But he hold his emotions back, and launch his final and unique form "Flaming Thunder God" and beheaded him in a flash.

You can say, "Oh, he was a newbie" and the weakest of the upper moon, but as I mentioned before, if he is, he wasn't able to make as an upper moon in the first place.

The technique "Flaming Thunder God" was created by Zenitsu himself to fight alongside with Kaigaku, but ended up by killing him. And this attack was so powerful that even Kaigaku, who's Thunder Breath got stronger by blood demon arts, can't react to his attack. By this attack, he create a dragon like creature which emits fire and thunder. I think this attack is inspired from Inosuke's "Breath of Beast" as the dragon is known as the pet of Raijin, the Thunder God. And this attack also consists "Flame" so he might be inspired from Tanjiro's Hinokami Kagura". Even the Japanese translation of this attack have Hinokami in it "Honoikazuc-hi no Kami."

He also broke the rule that only Hashira power level demon slayers use the sword which has kanji character in it. And he's sword colouring is cool! It's a blacks nd white blade with a yellow lightening pattern on it. But when he starts fighting, the white side changes into golden too! And it turned into gold colour permanently after his fight with Kaigaku. This fight while Zenitsu's power matched with a Hashira without the required the sword maybe symbolises that there will be no new Hashira. And the lightening pattern is similar to kentsuki:- a Japanese repairing method in which broke area is joined with an adhesive which is made by mixing laquer with powered gold.  

In this fight, he became one of the rare non Hashira who doesn't match only 1, but 2 feats same as a Hashira
1. Created an original form, unique to himself ( by Giyu Tomiyoka and Muichiro Tokito)
2. Defeat an upper moon by himself (by Muichiro Tokito)

After the fight with Kaigaku, he fainted from blood loss, and he was able to met his Gramps for the last time in afterlife. The two were opposite side of a river, and the banks are full of red spider lilies. He apologized for not answering his letter, and not to get along well with Kaigaku. He also told that Kaigaku never became a demon if he wasn't alive, or around them, just like how Tanjiro feels when he was unable to protect someone. He tried to cross the river to reach his sensei, but the red spider lilies tangled up with his feat, saying not to die. Just then, Jigoro said his last words to him:-

"Zenitsu, you are my pride and joy"

Tears filled up their eyes, and Zenitsu came back from afterlife, and he got the meaning of his name, "goodness".