User blog comment:Purpled/Cross-character cross-synth's legality/@comment-24785637-20150215190409/@comment-24684900-20150215195835

You can cross-synth vocaloids like Miku Solid and Miku Dark, however cross-synthing between say, Chika and Gumi is not allowed since you essentially have to trick the program into cross-synthing between the two by changing some of the files. That is what I'm referring when I mean that cross-synthing between characters being illegal, if that clears up any confusion.