To provide knowledge of the 'meta' real-life events concerning the C96 releases (referred to in-universe on the following page), as well as character development for some G-Spring characters.
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Anyhow, for this page, apparently it's a limited-release staplebound book featuring Goddess of the G-Spring characters in the Girls Who Get It setting. Think this is the only book with (mostly) exclusive content that one cannot find on the Twitter webcomics.