Ten enemies ranked zero to nine, each carrying its number tattooed somewhere on its body.
Filed by its count, not its title
Reduced as a phrase, “The Espada” would sit on The Inquiry — but that would be reducing wording this reference chose. The set is filed under 1 · The Opening instead, because 10 is what its author chose, and a chosen number outranks an imposed one.
The ten strongest of the antagonist's forces, ranked and tattooed. The numbering runs from nine at the bottom to one at the top, with a zero above that — a rank created to sit outside the scale it belongs to.
Ten is the number a reader already counts in, so the ladder needs no explanation at all. Tattooing the rank makes it inescapable: a character cannot be coy about their position, and every reveal of a number is a reveal of the fight's outcome before it starts.
The zero is the interesting move. Having built a scale where lower means stronger, the author needs somewhere to go beyond the top, and zero is the only honest answer — it is the one numeral that can be added to the bottom of the sequence while sitting above all of it. It is also an admission about ranked sets generally: they run out, and an author who wants more headroom must either break the scale or extend it into a place it was not designed to reach.
The Japanese name is 十刃, ten blades, which states the count and the weapon in two characters. The Spanish espada is a pun on it — the series' Hollows carry Spanish names throughout — and the two readings land on the same number by different routes.