Artist's commentary
Suletta the Rock!
It's the Depressing Happy Birthday song, sung by Suletta Mercury.
[Twitter: twitter/michirushiduki]
[Twitter for adults: twitter/michirushidukiR]
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[Melonbooks: https://www.melonbooks.co.jp/circle/index.php?circle_id=21745]
[FANZA: https://www.dmm.co.jp/dc/doujin/-/list/=/article=maker/id=72852/]
[DLsite: https://www.dlsite.com/maniax/circle/profile/=/maker_id/RG18481.html]
[BOOTH: https://bijyutsubu.booth.pm]