The Sun Pillar
Summary: Kamado Tanjirou's journey to become the Sun Pillar and take down Kibutsuji Muzan.
Notes: Seen through Tanjirou's point of view and following the manga closely. Might feel a bit OP – and/or OOC – in places, but I tried to keep it believable. A huge AU project, that didn't want to leave me. Slow-ish and irregular updates, because I am doing some extra beta work on it.
Chapter 1: Prologue
The Kamado family had always been part of the Demon Slayer Corps, rumored to carry the original Breath on from its first user. Because of that they were considered the leaders of the Pillars.
They were always on good terms with the other Slayers and the Pillars. It was their kind personalities that endeared everyone to them.
Until Tanjuurou, the Kamados were a force to be reckoned with.
Unfortunately, an illness weakened the head of the Kamado family before his time, forcing his eldest son, Tanjirou, to slowly take over the role of the head of the family from the young age of eleven. He would officially be the head two years later, at the age thirteen.
If it weren't for the Flower Pillar's younger sister, Kochou Shinobu, Tanjuurou would have died a couple of years earlier and way before his time.
Still, Tanjirou had to go through the Final Selection at some point, and it was decided he would when he was fifteen, since he needed to learn of his duties as the head of the family along with his corps training.
He was eleven when the news about Kanae-nee reach them.
Tanjirou bolts, running all the way to the Butterfly Estate, as the acting head of the Kamado family and the next Sun Pillar, but mainly as a family friend to the Kochou sisters.
He had last seen them only two days ago, had wished them safety and luck, asking them to be careful, promising to come and see them when they'd return.
"Shinobu!" he calls, as he reached the Estate.
He doesn't wait for an answer, his call was more of a warning than anything, letting his nose lead him to the girl.
Shinobu has barely a second to recognise him when he crashes into her and hugs her so tight, one would fear for broken bones.
"I'm so sorry!" he cries, "I'm so sorry, Shinobu!"
Slowly, Shinobu wraps her arms around him, returns the tight embrace.
"Tanjirou-kun…?"
"Yes." he hiccupped.
"I…I miss her. I miss nee-san, Tanjirou-kun."
He staid with her, Aoi and Kanao, his family coming later in the evening.
Tanjirou didn't leave her side. They practically cried themselves to sleep.
It was the second to last time Tanjirou saw Shinobu express her feelings so openly. The last was at Kanae's funeral.
He staid behind, afterwards.
"I'm sorry, Kanae-nee. I promised you to be there, to become a Pillar and fight at your side. I'm sorry I wasn't fast enough to make do on my promise. But, I will look after Shinobu. I'll protect her, I'll protect them all, no matter what. I won't fail you again. I promise." he said quietly, wiping his tears, "So. So, please look over us." he asked before leaving.
He never noticed he wasn't alone.
Notes: The decision for Tanjirou to enter at the same age as the manganime, has to do with the fact he has to balance Corps training with coal-burning and family head duties.