"And as a wise man once said, and I believe this to be true: Marcille Donato has two hands".
Even if one is... let's say, more socially-awkward than the other, Laios Touden and his little sister Falin are ultimately like two peas in a pod, both in terms of appearance and interests, which is more blatant when they interact. One could even say they're like two perfect slices of bread; so much so, in fact, that some artists love drawing them sandwiching other characters, Marcille almost always being a prime "victim", thanks to her closeness (the romantic or platonic nature of it is left purely to interpretation) with both siblings.
The "Touden Sandwich" usually has strong romantic and/or sexual connotations, but it also qualifies when its depiction is perfectly platonic or ambiguous. See post #7291931
Contrary to what that first quote implies, and even if it rarely happens, the sandwiched character doesn't necessarily have to be Marcille to qualify for this pool. See post #7515689