Kokoro from 'Vocaloid' is such an underrated gem, and I totally get why fans would want her in 'Project Diva'! From what I've dug into, she hasn't made an official appearance in the mainline games yet, which is a bummer. But here's the cool part—modders have created custom charts for her songs, so if you're playing on PC, there's a way to experience her in the game unofficially. Her melancholic tunes like 'Kokoro' or 'Tori no Uta' would fit so well with 'Project Diva''s rhythm mechanics. It's a shame Hatsune Miku's crew dominates the roster, but maybe one day Sega will surprise us!
I’ve spent hours scrolling through fan forums, and the demand for lesser-known Vocaloids like Kokoro is huge. There’s even a petition floating around—though I doubt Sega’s paying attention. Until then, I’ll keep dreaming of a 'Project Diva' expansion with more niche Vocaloids. The community’s creativity with mods almost makes up for it, though!