The manga's organization is explicit: thirteen divisions under a captain-commander, each captain (taicho) and lieutenant (fukutaicho) in marked uniform, captains distinguished by white haori bearing the division insignia. Kubo's stated aesthetic intent is equally documented: he created the series because he wanted to draw Soul Reapers in kimono, a version of the Japanese past nobody had drawn that way before. The courts, the wooden barracks, the ranked martial bureaucracy: the afterlife is Edo, bureaucratized.
The fan case: the Shinsengumi were also a numbered squad system of swordsmen under a commander, Kondo Isami, wearing signature haori, policing a capital, torn by internal factions, betrayals, and purges, and ended in noble annihilation. Bleach's first arc, a captain condemned, factions splitting, a rescue against the courts, rhymes beat for beat with the Shinsengumi's own legend of loyalty against the state. Fan essays have mapped captain to captain for twenty years.
The esoteric observation: a corps of death guides numbered thirteen, the West's unlucky number and the tarot's Death card, in a series whose author hides jokes in doorplates. Fans note that squads are sorted by archetype, healing, science, stealth, brute force, like a minor arcana, and that the first thing the story does is shatter the thirteen's unity from inside.
If the mapping is so exact, why does it live only in fan essays and never in an interview answer, and does an unacknowledged model count as an origin?