@Gel *You're welcome.* That said, the Weapon File doesn't discount it being its own weapon, and possibly a devil. It gives Vergil (and the specter behind Nero) a sheath on his left arm, a quality lacking in the actual Sparda sword and his devil form, and the Devil Bringer's scales match the design of the hilt. That doesn't have Sparda's direct influence (unless the Yamato is "a Sparda" but that's headcanon territory). Sparda sealed Hellgates with it and his blood, but it's not
from him the same way his own Sparda sword is, or how Cerberus is made from Cerberus, etc.
To answer the topic, not even Capcom can figure out what Rebellion is.
It made its debut in DMC2, where it was described as:
Devil May Cry 2,
Weapon File — Rebellion: "A standard sword for Dante." As unremarkable as the Merciless or the Vendetta.
Then DMC3 showed up and retconned its position (replacing the Force Edge) as:
Devil May Cry 3, Code: 1 — Dante,
Dante's Weapons — Rebellion: "A keepsake sword from his father. Its name means "resistance." The game adds "This magic blade's true power hasn't fully awakened"/"Dante's blood has awakened the blade's true power."
In comes DMC4 and:
Devil May Cry 4,
Dante's Arms File — Rebellion: "A memento given to Dante by his father, this large magical blade is the physical manifestation of Dante’s power."
So it's somehow a physical manifestation of Dante's soul/power, but it was held by his father previously. Sparda had his son's soul? And then it just becomes a standard sword in the future?
That and Devil Arms are usually named directly after the devil that possessed the soul. Cerberus was named after Cerberus, Nevan was named after Nevan, Vergil pulled the Beowulf out of Beowulf, Sparda "wield[ed] a sword that bore his own name", and while we don't see Alastor and Ifrit's forms as their own, they look markedly different from each other when Dante uses their Devil Triggers in DMC1 and neither of them resemble the Sparda DT from the second-to-last mission. Dante has no reason to make
himself look like a spiked cyclops just because he's wielding fire gauntlets, so that's Ifrit's real form, and Alastor's is Alastor's. That said, if Rebellion were the equivalent of Dante's personal DA and a manifestation of his soul specifically (as opposed to literally anything else, like a demon that Sparda stripped of its true name, renamed Rebellion, and bound to his blood), it should
probably have his name on it for consistency's sake but it doesn't and Capcom won't get around to explaining it.
Not all Devils turn into Devil Arms, but if it
is a Devil Arm, then there's a really good chance it was a Devil beforehand. That's how the series shows it.
@Goldsickle He doesn't sell them. The DMC Anime Drama CD featured him summoning Alastor to subdue a possessed Lady, using Cerberus to deflect her bullets, and Patty and Enzo converse with Agni and Rudra. So he keeps those weapons in a room somewhere to summon whenever he needs them. Then the DMC4 novel has Gilgamesh, Lucifer, and Pandora as weapons he had before the game even started, so he didn't sell those either and he doesn't have a debt in that game anymore (Lady pays them for the mission).