Senjuro's age: nearly 15

Months later, it was finally over. Muzan had been defeated and the Demon Slayer Corps was, at long last, victorious. A significant portion of the world's evil was no more.

As Senjuro sat outside in the yard of the Butterfly Mansion, he wished his brother could be here to see it. Kyojuro had fought so hard and yet he'd never be able to experience the payoff. None of the Slayers who'd died would be able to celebrate the victory over the demons.

And yet Senjuro, who had done nothing to help bring this victory about, had survived. He hadn't been a Demon Slayer - he hadn't even been a Kakushi. And yet it was he, not Kyojuro or any of the other fallen Slayers - not even most of the Hashira - who had survived. Why? Was it just some stroke of fate that protected him? Was that all that ever determined who got to live and who didn't? That seemed so wrong, so completely unjust.

The sound of footsteps shook him out of his thoughts, and he looked up to see who was approaching. Father.

Father sat down beside him on the ground. The bags under his eyes were as heavy as they'd ever been, and his cheeks were covered with stubble, but there was a looseness to his shoulders that Senjuro still wasn't used to seeing. He cleared his throat, looking like he wasn't quite sure what he was doing. "It's, uh, a nice night, isn't it?"

"Yeah," Senjuro nodded. That night could be nice was a miracle. Now, it could mean something other than near-constant danger. Nights no longer had to be spent wondering if any demons would try to break into the house. Nights could be spent outside with nothing to fear.

"I wish…" he started, then paused. Though he and Father had spent the past few months relearning how to be a family, they'd mostly carefully avoided the Kyojuro-shaped hole in their lives. Was bringing him up now a good idea, or would it lead to another setback?

This was a time for new beginnings, he decided, and he didn't want to lose Kyojuro to the future. He was determined to keep his brother alive however possible. So he pressed on, "I wish Kyojuro could be here to see it."

Father sighed, his head bowing and shoulders slumping. "I do, too."

Encouraged by his response, Senjuro continued. "It's not fair," he said, some of his anger and grief slipping into his tone. Those emotions had existed for months, bubbling just beneath the surface, and he was too tired to hide them anymore. "It's not fair that we get to live and he doesn't. I - he's the one who fought for this. I did nothing!" He shook his head as tears stung his eyes, then spilled over.

He didn't care. He just needed to get these words out. "And I just - I hate it! I hate that he fought so hard and now he can't even be here to see what the world looks like without demons! He's gone," he said, his voice, which had started out strong, fading into a whimper, "and he shouldn't be. He shouldn't be gone - I don't want him to be gone."

Without a moment's hesitation, Father pulled him into a hug. At first, they both stiffened in surprise, but gradually, Senjuro relaxed and Father did too. "It's not fair," he agreed. "It's not fair at all."

But being unfair didn't make it any less real. As much as he wanted to reject the way things were, life didn't work like that. The dead could not come back to life.

He knew what Kyojuro would say - he could even hear it in his brother's usual enthusiastic tone: "You can't change what's already happened, Little Flame, but you can still work to make the future better!"

But right now, that prospect seemed incredibly daunting. He was barely coping with everything that had happened - he could hardly start working toward the future.

He let out a sigh, slumping a little more against Father. It wasn't quite the same as a hug from Kyojuro - Kyojuro had given the tightest, warmest hugs he'd ever experienced - but it was still nice.

But maybe that was okay. Maybe it was all right to need this time to absorb everything and figure out where to go from here.

"He was a good son," Father quietly said. "You both were. Are." He grunted, shaking his head. "Much better than I deserve."

"You were mourning Mother," Senjuro replied.

"Still," he sighed. "I doubt I'll ever make up for how I treated both of you."

Senjuro was quiet for a moment, considering. He thought of all the harsh things Father had said and done. Though he knew they'd come from a place of grief, not genuine malice, he couldn't forget how much it hurt every time. But Father was trying now - he hadn't touched a jug of sake in months, even when the withdrawal symptoms were at their worst. And that was something - a lot, actually. He only wished Kyojuro could be here to see how Father was finally starting to heal. "Maybe not," he acknowledged. "But you can't give up now. We'll take every day as it comes, okay?"

Father huffed softly. "You sound just like him."

He did? He'd never thought of himself as especially similar to Kyojuro. He was quiet while Kyojuro was bold. Kyojuro was the strong one, the one who wasn't afraid to speak his mind or make a decision, while he was the one who did his best to be unobtrusive. But he'd learned more from Kyojuro than just how to wield a katana.

And that meant Kyojuro was a part of him. And he would do his best to be the same sort of person Kyojuro had been: kind, a protector, someone people could look up to. That would keep Kyojuro's memory alive.

And maybe…maybe that was what he could do with his future: help people. It would be maintaining Kyojuro's legacy while also being something he'd wanted to do his whole life but had never been strong enough to accomplish. He would live up to Kyojuro's nickname for him, Little Flame, being a warmth and comfort for those who needed it.

He liked the sound of that. He might not know how he was going to do it yet, but that was okay. It was a start, and for now, that was enough.

The End

Notes:

-A HUGE thank you to Shelley for helping me edit this even though she's not familiar with Demon Slayer!

-I made myself sad while writing this.

-The first conversation (but not the dialogue itself) between Senjuro and Kyojuro, as well as the mention of how Kyojuro became a Hashira, are both based on parts of Kyojuro's story in Stories of Water and Flame.

-Senjuro's age throughout is largely based on very rough guesses, although he was definitely around 14 when Kyojuro died.