We do know that Inosuke has official uniform pants, two Nichirin swords for choosing two tamahagane, and a crow (poor crow who hides his presence cleverly, because if Inosuke notices him, he might be eaten). Inosuke put on the top of the uniform fine, but it was so uncomfortable that he ripped it off, tore it to tears, and then trampled her, according to the textual secrets of the first fanbook. As a result, his uniform designers despise him as much as they despise snakes and scorpions.
When Inosuke joined the Final Selection, he understood what he was getting himself into; joining the Corp was an opportunity to show his strength, and it also meant following what it meant to be a part of this pack. It is, however, a learning process. Defeating demons is a simple rule to follow, and if he understands the finer points, such as not drawing a sword on other Corp members, he’ll gladly comply and stand up. Instead, beat with your hands.This meant that he had a good understanding of the basic rules of Final Selection, and as soon as the day came on the final day, he was in a rush to go prove he was the best. The first to finish, even!
Zenitsu heard him but didn’t see him as he descended the mountain. He notices something in front of the demons’ house: “Ah…!” He’s the one! I recognise him now that I’ve heard his voice. This is the fifth person who has been successful! This guy who went up the mountain and came down the mountain much ahead of everyone else! The really impatient individual! And that was only after Inosuke smashed his head through a door while screaming “Pig attack!” AHAHAHAHAHA! While a result, it’s safe to infer he was saying similar things as he climbed Mount Fujikasane.
So this is what I believe happened. We only saw things from Tanjiro’s vantage point on Mount Fujikasane, and when he arrived, there was already a mob of kids, including Zenitsu. Inosuke was probably there long before that, exclaiming that he was one step ahead, maybe a few words about feeling the presence of the demons he’ll be slaughtering for the next week, and maybe ASSAULT OF PIG. While Zenitsu may have thought “dumb,” Kiriya and Kanata may have felt “it’s still early, but we’re not going to stand in his way.”
Inosuke then laughs and comes down the mountain, saying that he is the best, at the first light on the seventh day. “Is this guy still alive?” Zenitsu asks himself. Inosuke reunites with Kiriya and Kanata and informs them that he has won the competition and has joined the Demon Slayer Corp. They compliment him. When he asks, “What do I get now?” they explain everything to him right away, in the same order.
They begin by taking his uniform measurements. “How do you define a uniform?” Is it safe to eat? He would have inquired, and they would have explained that it is a durable clothing that identifies him as a member of the group. Inosuke is puzzled and a little excited, because he’s never had any unique garments before, except from his fundoshi and boar face. A uniform could be entertaining (no, it won’t). It works in tandem with measurements.
We then tell him about the levels and that he is a Mizunoto. “How will I know when I’ve reached a higher level?” When Inosuke inquires, they explain how to make a fist and request to be demonstrated. He thinks it’s brilliant and tries it out, but he still can’t read it. Every time he changes, he’ll keep pestering people to read it for him. (Tanjiro did not inquire.) Maybe Tanjiro was never informed. Or, more likely, Gotouge forgot about it until later, when it was more convenient).
Then they tell him how a Nichirin blade will be made for him with the tamahagane of his choice. He chooses two. Kiriya and Kanata think there won’t be enough survivors to run out of tamahagane options, so they agree. Inosuke finds himself brilliant for outsmarting them.
They promise him that the swords and outfit would arrive in 10 to 15 days, and that he will be assigned his first task then. Inosuke is frustrated at having to wait so long, so he proclaims that he would go kill other demons right away (despite Kiriya and Kanata’s protests because the sun has just risen), and he rushes down the rest of the mountain. They send a crow after him in a rush so they don’t lose track of where to give his stuff later. Fortunately, the crow is a skilled Kasugai-garasu, albeit he will find this relationship challenging.
Then Zenitsu arrives and hears cackling coming down the mountain from afar. He doesn’t want to look silly, so he decides to wait and regain his breath, not looking forward to hearing what else is in store for him. Not receiving a call, Kiriya and Kanata simply smile and stare till Kanao, Genya, and ultimately Tanjiro arrive. This is hardly a particularly unsettling start for the agency’s members.