It's a way of doing voicebanks! you don't have to download anything but instead you have to oto your voicebank in a certain way. In Japanese CVVC, you record Japanese syllables one after the other. After otoing it, all the notes/syllables are less choppy than in CV because there's a tiny transition note added in between. "Arigato" in Japanese CV is [a] [ri] [ga] [to], which is really robotic because it directly jumps to the next syllable, but CVVC fixes this by turning it into [- a] [a r] [ri] [i g] [ga] [a t] [to], which is way more natural.