He said as much in his 3D after party. Paraphrasing: Management came to him to ask what he wants to do for his 3D, he jokingly brought up Miku but nothing more was said on that occasion. Some weeks later his manager writes something along the lines of "So about your Miku performance, here's the contact information and such, this person will make it happen". He said it was the most expensive thing he's ever done but I don't think he paid list price since it was only a stream and he had an in through Anycolor.
On this weeks episode of "Why bother with the vague posting anymore?"
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They should just tweet at each other and see what happens, not much different to this anyways.