/jp/ - Otaku Culture

I know nothing about Vocaloids at all, but feel I have missed out a lot and can’t get any info so if you guys have any I’d love to know.
Regardless, I have played this game called Cogen Sword of Rewind that was released recently, I can’t find much of the game and its connections to Vocaloid, but apparently Kohaku Otori is a Vocaloid actually, Akasha the AI is known as Akaza and the whole game seemed like some sort of reference to one of their songs? Or at least that’s what seemed like by the characters talking near the end and some poem about a Devil and a wounded bird that had to free the world.
I don’t get much whenever I search in english, but do you guys know what this was all about? Is Cogen a big Vocalois reference, was this actually planned, a joint project of sorts? Do Vocaloids tend to have storylines like that in futuristic settings?
It’s just after beating the game it felt there was part of this context I have missed. In particular with a few teases with Kohaku mentioning having already survived a plane crashed before the events of the game and fought aliens and the like.