⚠️ Warning/s: Spoilers - if you haven't finished Demon Slayer yet ⚠️
Flashback:
Before stepping foot out of the house and on my way to my mission, I made sure to check all of my supplies and ensure that I'd be ready for any challenges I might face. Asaki perched on my shoulder as I fed her some food before she took off and led the way towards the meeting point.
Y/N POV (Present time - Age 14):
Well, now it was time to go on the mission with the squad and Rengoku. Asaki told me the nature of the mission: a demon responsible for killing many low-ranked demon slayers on a train, leaving no traces behind. They have requested backup from headquarters and so we have been sent out as help for Rengoku as he answers the distress signal.
Honestly, I had an underlying bad feeling, and I tend to be right with my hunches. Upon arriving at the train station - which we previously decided would be our meeting place - everyone was already there. We all embarked on the train ready for a new mission, one full of anger and tears, as far as my senses tell me.
"Umai!... Umai!" Rengoku yelled while eating his food with a routine: picking up the food with his chopsticks, eating the food he picked up, then yelling 'Umai' after each mouthful.
Meanwhile, Zenitsu was desperately stopping Inosuke from jumping out of the window, and Tanjiro was trying - and failing - to talk to Rengoku while he eats. He mentioned a breathing style I had heard of before in my reading, the 'Sun Breathing'. It seems that almost no one knows about it, but the library where I learned about it was secretive.
The reason that I haven't told Tanjiro what I know is because of what it entails, and I am unsure why he would need such information. Most of what I have read is about the ancestry and history of some breathing styles, Sun Breathing and Moon Breathing to name a few. It mostly tells me who was the first user and creator of the breathing style/s aka. Yoriichi Tsugikuni and Michikatsu Tsugikuni aka Kokushibou (Uppermoon 1). Yes, I am aware that Michikatsu becomes Kokushibou as they stopped writing about him when a new Uppermoon was announced as being seen with incredible swordsman skills.
Michikatsu was second only to his brother, Yoriichi. This must have fuelled some jealousy and then he might have accepted Muzan's offer, becoming a demon. Due to his high potential, Kokushibou rose through the ranks and became Uppermoon 1 as he kept his breathing style - Moon Breathing - while he was a demon.
However, Tanjiro didn't need to know about that as he wasn't a direct descendant of either of them. Yes, his family were friends with Yoriichi and they passed down his earrings and a dance called the Hinokami Kagura - the dance was actually Sun Breathing forms - but after a couple of hard missions then I'll tell him what I know. He's Yoriichi's successor, the successor of the man who almost killed Muzan before he fled, Tanjiro Kamado.
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Editing: Complete.