Demon Slayer: Kimetsu no Yaiba

[Ryllharu]

All we know is that they are more powerful than normal demons "on the street", yet we have no information about the difference in power inside the group itself.
It's probably similar to the Arrow and Ball demons that were kinda special? They did follow Muzan's direct orders yet even somone with the lowest rank inside the Corps (Tanjiro) was able to defeat them.

Muzan took two fairly new demons, pumped them up with a little of his blood, and told them they were Twelve Moons, when they 100% weren't. He lied to them. Their only purpose was to hunt Tanjiro and Tamayo because he had just encountered them both on the street.

That's how quickly he can make new demons that can give trained and experienced slayers trouble.

@MFauli:
No. The Hashira are just those demon slayers who have survived this long and trained to such extreme lengths to the point that they are actually consistently useful. They're the upper ranks of the slayers. They're all human. Tanjiro would have smelled something if Tomioka wasn't. Urokodaki was one too, same thing, Tanjiro would have noticed.
The regular ones survive the night on the mountain, maybe kill some new and weak demons, and they're in.