Aside from posting the making-of, the commentary and the picture theme is a reference to the (at least partial) etymology of their name/surname (the artist replied to an own message about that)

Hikari's surname Kagura means "god" (神) (ka) and "easy" (楽) (gura).

In Chinese, the first character of Karen's given name, 華 (ka), can mean corona, an optical phenomenon of a ring of light around the sun or moon. "Corona" is latin for "crown", and Karen wears a crown hairclip that becomes a small crown in her revue uniform.
This is likely entirely an etymological coincidence, as the usage of 華 (or 华 in simplified Chinese) does not relate to "crown" at all, but rather the brilliance or splendor of the phenomenon, and in Japanese, it is referred to as コロナ (corona), and there is no relation to the character 華.