Eight limits on the body, each of which can be opened for more power — and the eighth of which kills whoever opens it.
Filed by its count, not its title
Reduced as a phrase, “The Eight Inner Gates” would sit on The Turn — but that would be reducing wording this reference chose. The set is filed under 8 · The Ledger instead, because 8 is what its author chose, and a chosen number outranks an imposed one.
Eight notional restraints on human physical output. A sufficiently trained fighter can release them in order, gaining strength at each gate and paying for it. The last gate grants the greatest power available to a body without supernatural assistance, and the body does not survive it.
A ranked set is normally a roster of people. This one ranks a single character's willingness to die, which is a considerably more interesting axis. Because the count is fixed and known in advance, every mention of a gate is a position on a scale the reader has already internalised — the sixth gate means something specific, and it means it without a word of explanation.
It is also a rare numbered set that costs the author nothing to complete. There is no obligation to show all eight in use; the eighth exists mainly so the seventh has something to be short of.
The name is borrowed from Qimen Dunjia, a Chinese divinatory and military art whose eight gates are directional and cosmological rather than anatomical. The manga keeps the eight and the vocabulary, and discards the system — which is roughly how most numbered sets in this section relate to their sources.