Chiruran: Nibun no Ichi

Shows based on Vocaloid originals or involving utaites/producers who are/have been active on Nico Nico Douga (extended to YouTube for newer gens).
While not its own genre, these compositions tend to have a recognisable feel to them.
(Updating as I come across songs, you can poke me to add stuff as well :D)

2nd stack for post-2020 anime debuts: https://myanimelist.net/stacks/26372

Actual Vocaloids:
GUMI ~ Joshikousei no Mudazukai / Agukaru: Play with Ibaraki-hen
IA ~ Recorder to Randoseru Mi☆
Miku ~ Akikan / Watamote / Yami Shibai / Black Rock Shooter / Kemurikusa / ALFA-X / Aware! Meisaku / Petit Seka
MEIKA Hime & Mikoto ~ Hakata Mentai! Pirikarako-chan
Luka ~ Copihan
Meaw (possibly) ~ Honto ni Atta! Reibai Sensei
Go! Go! 575
Zunda Horizon

Prioritising first appearances/multiple artists bc of 50 limit. For composer entries, the singer is only listed if they're
At some point, I'd have been super hyped for any show with a Vocaloid producer but come late 2010s they've been popping up everywhere :')

*List is roughly sorted by anime based on Vocaloid songs > Male utaites > Female utaites > Producers