Enter: Universe Breathing! (Demon Slayer Reader)

Setting Off! A New Mission!

(y/n)'s POV

Today Zenitsu starts the rehabilitation training. Tanjiro and Inosuke walk with the same dread as they did when I was starting. Suffice to say, Zenitsu was affected by the dread Tanjiro and Inosuke radiated. I, however, was just lazy and wanted to get this over with. 

"H-Hey..." Zenitsu says nervously. "You guys are scaring me. It's not that bad right...? Guys?"

We arrive at that all too familiar room. Aoi gives Zenitsu the run-down, much like she did with me.

However, right after Aoi finishes, Zenitsu's fear is completely gone.

"Hey..." Zenitsu says. "Come on, both of you."

"Huh?" Inosuke says. "No way, I'm not moving."

"Shut up and come with me like I said!" Zenitsu yells.

Zentisu then grabs Inosuke and Tanjiro by the collar of their attire and starts dragging them out of the room.

"Come on you lowlife dirtbags!" Zenitsu yells. "And you! (y/n)! You better come along too! Your attendance will decide their fate!"

Zentisu continues dragging them out of the room and towards the yard. Of course, I would've preferred to stay inside, but I didn't really have a choice, so I followed their trail.

"You bastards!" Zenitsu screams. "You're both miserable bastards!"

"Huh?!" Inosuke says. "What did you say?!"

Not even a second after Inosuke finishes his sentence, Zenitsu nails him directly in the face with a punch, sending him flying into the wall behind us.

"Inosuke!" Tanjiro cries out, aiding his friend.

"What the hell Zenitsu!" I yell back, helping Inosuke. "That was just plain rude! Apologize!"

"You guys apologize to me!" Zenitsu yells back with enough force to knock Aoi off her feet. "How dare you all come back from training acting like you returned from Hell when you were actually in Heaven?!" Zenitsu screams.

"All you did was play and frolic with girls all day!" Zenitsu yells, jumping around wildly. "Get on your hands and knees and apologize! Commit seppuku!"

This goes on for a while, and eventually Zenitsu calms down and happily frolics back to the training room.

"Hello!" Zenitsu says with a smile, basically radiating pure bliss. "Please teach me well!"

Zenitsu easily survives the stretching portion, laughing throughout the entire ordeal. Then, during the cup game, he easily outspeeds Aoi and puts the cup right in front of her. However, he doesn't splash it on her.

"I would never splash tea on a girl." He says, irritating Aoi.

Finally during tag, Zenitsu easily tags Aoi too. Except, he goes a little too far and full-on grabs her as if it was a hug, earning him a beating from an irritated Aoi.

"I won the battle but lost the war!" He says. 

(Timeskip)

It's been a while since Zenitsu's time training started. It's a long story as to what happened every day since then. But to summarize, everyone except for Tanjiro, including myself, lost all motivation to continue training and stopped doing so for a while. It wasn't until we all witnessed Tanjiro's tremendous growth that we also trained like hell.

In the end, we all mastered Total Concentration: Constant, and were given the final test.

"Now's your final test." Aoi says, presenting four large gourds. "You've mastered Total Concentration Breathing Constant, I'm impressed, some more than others."