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Artist's commentary
Belly button creampie
(I want to do it~~~~)
(High-resolution version + variant at FANBOX https://rakuukrk.fanbox.cc/posts/1034352)
While へそだし (臍出し, aka intranavel ejaculation) has no real-world equivalent, it is exactly like 中出し (nakadashi, literally meaning "letting out inside"), so I've translated it as such.