I've came to learn that there is an A4 clear file released on Comiket 88 alongside the artbook where you can peel the top clothes layer revealing the girls wearing skimpy bikinis.

https://www.suruga-ya.jp/product/detail/984905295

How it looks hands-on (GIF):

https://arch.b4k.dev/v/search/image/cdFi1QUjC3W5rzOITCu2_g/

I hope someone scans and upload it, would be a crying shame for such sexy lolis to be lost media.