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Artist's commentary
Two immature girls at the onsen
Drawing multiple people really takes a lot longer. Maybe I should've stuck with just Raimu-senpai...
The title contains a pun. "Otonagenai" means immature, and is normally written as "no adult spirit" (大人気ない), but here the "ge" is written with the kanji for "hair", so the phrase is read the same way but is written as "no adult hair".