By the way kappa have 3 XX "Other inhuman traits include three anuses that allow them to pass three times as much gas as humans..."

Flandre's wraparound skirt

It looks like a white clip of a wrapped skirt

It's pixelated but this confirms it

Flandre's Spell Card Background (With color correction)

A curtain like form is here

The shadows look like vertical stripes?

Patchouli's original style isn't vertical stripes

In ZUN's original style it doesn't look like vertical stripes

The Komeiji sisters' innerwear

In their ragged post-defeat pictures, the sleeve frills and underwear are the same color.

It becomes innerwear like in the below illustration?

The frog hair ornament on Kochiya Sanae is a hairband

Kawashiro Nitori's hairclip has at least 3 balls