1 pointAs seen on the lyrics, in the description or in closed captions on the youtube video, it is Detective Detective.
1 pointAlso, in "I'm sorry!" Someone- either the detective or Cole, says "Ugh, you've GOT to be kidding me." if it is the detective, that means that the meeting between Star Blush and Meteor wasn't planned, as you said. If it was Cole, your earlier theory about it being planned still makes sense. though, i believe it IS the detective saying it, as the detective is the main speaker throughout the entire song, save for kanesaki's apology.