Majin Bone

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/Other voiceroids:
GUMI ~ Joshikousei no Mudazukai / Agukaru: Play with Ibaraki-hen (cv: Megumi Nakajima)
IA ~ Recorder to Randoseru Mi☆ (cv: Lia)
Miku ~ Akikan / Watamote / Yami Shibai / Black Rock Shooter / Kemurikusa / Shinkalion ALFA-X / Aware! Meisaku / Petit Seka / Ani × Para (cv: Saki Fujita) / Nmeneko
MEIKA Hime & Mikoto ~ Hakata Mentai! Pirikarako-chan (cv: Kotori Koiwai)
Luka ~ Copihan (cv: Yuu Asakawa)
galaco ~ Classicaloid (cv: Kou Shibasaki)
VY1 ~ Genshiken Nidaime
Kasane Teto ~ Gnosia

Meaw (possibly) ~ Honto ni Atta! Reibai Sensei
Go! Go! 575
Zunda Horizon

Luo Tianyi ~ Wan Sheng Jie (JP version features CevIO AIs Satou Sasara & Suzuki Tsudumi)

Prioritising first appearances/entries with multiple artists because of 50 entry limit.

*Grouped by: Anime based on Vocaloid songs/themed media > Male utaites > Female utaites > Producer units > Producers & sorted oldest to newest in each category

Anime that ran for approximately a single year. Episode counts including 45-55. Japanese anime only.