Oh, so their outfits are sort of apron combos...how risque.

What's interesting is that, unlike the majority of the teams, their costumes actually match.

That's actually a trend amongst the teams who aren't 'Default'.

Suika + Sakuya have the bottom aprons and a maid motif.
Cirno + Yuuka have fairly simple school swimsuits.
Reisen + Youmu have the sort of bunny valet vests + gym leotards.
Utsuho + Tenshi have the naked apron + not exactly naked but not covering the goods outfit.

The others seem to be content to have outfits based on their usual costumes primarily, without any concern for any kind of matching theme.

Dei Shirou is an evil genius.