The demon's apprentice

Boredom

Muzan was obviously furious. Hantengu and Gyokko were defeated only two months after Daki and Gyutaro. The embarrassing part was that Hantengu burned in the sun. He hadn't reached shade in time and burned. Pity. Gyokko had been defeated by a kid. Embarrassing.

But no matter. Soon after they died, Nakime had found a way to figure out Ubuyashiki's hiding place. Muzan instructed the remaining uppermoons to stay in the infinity castel until Nakime would find Ubuyashiki.

This change in the routine bored Tanjirou. While the confusing nature of the infinity castle did distract the young demon enough to not be bored all the time durning his free time, he also wanted to see the outside world. It had been a while since he and Kokushibo had went out and now he was stuck inside.

Most of the time when he wasn't training, Tanjirou would jump around in the infinity fortress, seeing where he'll end up this time. Sometimes Nakime might decide to entertain Tanjirou a bit and move the castle even more than usual, creating a small obstacle course for Tanjirou.

Still, Tanjirou wanted to go outside every once in a while.

"Sensei?" Tanjirou spoke.

Kokushibo turned his head towards Tanjirou, implying that he was listening.

"Why can't we go outside?"

"He has... ordered us... to stay... inside for... now. Soon... everything will... go back... to normal."

Tanjirou stayed quiet for a while, progressing Kokushibo's answer.

"Can we go outside then? To the forest?"

Kokushibo nodded and Tanjirou smiled. His smile wasn't bright or big, it was small and soft. The boy's eyes began shimmerring slightly at the though of going outside.

Maybe one day, the boy will be the bright kid he might've been.