This is tagged "Azumanga daioh" because of the uniform, but the "original" tag suggests that this is not Chiyo. Also, she only kinda resembles Chiyo.

So is this just some artist drawing original characters that happen to attend the same school as the girls from Azumanga? Awesome.

She is Nemuro Nao's original character.
She has exactly the same name with the artist, but she does not seem to be a fictional persona.

Maybe it's his personal character cosplaying Azumanga Daioh?