The story is about how Yato met Rabo. If I'm not wrong, this manga was included in one of the Season 1 limited edition Blu-ray's. Rabo was an original character made for the anime, so Adachitoka decided to make a small backstory manga about him.
The manga is really short, only 2 chapters, but it's enough for an interesting backstory for Yato' character. The characters in Noragami are really likable and interesting.
The art is still as detailed and nice as always. With good backgrounds, character expressions and action.
I can definitely recommend this for any Noragami fan.