This brings up a question: How exactly does Flandre sleep with those wings?

On her stomach or side, as pictured above?

She's not on her stomach. She is on her side (same way I sleep).

I would imagine that all winged humanoids to deal with such things. Though I guess it's worse for Flan since her wings have pointy crystals on them.

Ah, good point but I pose this question: Whoever said that her wing crystals were hard? They could be soft and squishy.

Because they look like crystals.

That said, I imagine Flan' has it easier then, well, the vast majority of people with wings that can't disappear. Pretty much two flexible sticks with ornaments as opposed to, well... Giant bird wings.

I usually think about Suika having an issue sleeping. It's a good thing Flan doesn't have Suika's horns, otherwise the only possible sleep method is face-down.