This is spin-off. Not a prequel of the main story of Coton Candy. It's about a side character, Bun-chan, and her past. It have nothing to do with the story of Cotton Candy.
Well, that’s cutting the distinction between “prequel” and “spin-off” mighty fine, and I’m not sure what making it accomplishes.
Bun-chan’s chill, down-to-earth attitude as a love advisor to Mii was an important part of that earlier story, and now (I assume) we’re going see what her previous experience had to do with creating her present-day demeanor. So it has at least something to do with Cotton Candy.