★Rock Cannon

The ★rock Cannon is the name of the very large gun used by Black★Rock Shooter. There's also a similar weapon used by White Rock Shooter in her other form (as seen in her intro).

Appearance
It can be guessed that the trigger and handle to shoot is inside the gun because of the way Black★Rock Shooter attacks with it. Unlike Black★Rock Shooter's wielding style, White Rock Shooter seems to be holding it differently, pretty much how she holds her scythe in battle. The actual length of the ★rock Cannon is undefined, as sometimes it's shorter (in the song, OVA, and in the original illustration by huke) and sometimes longer (in a certain illustration and in the figma).

Black★Rock Shooter OVA
Not much is known about ★rock Cannon, only that Black★Rock Shooter obtained it somehow after the fight between her and Black★Gold Saw, possibly to replace the Black Blade she may have lost in the fight. She is seen walking around the Otherworld with it and fighting Dead Master with a giant blade that she was able to transform ★rock Cannon into.

Black ★ Rock Shooter THE GAME
Black★Rock Shooter obtains the ★rock Cannon after being awakened in her stasis tube along with the Black Blade. The weapons might be an invention of Prof. Gibson. The weapon have a bayonette attached to it so that it may double as an effective close-range weapon when Black Blade is unavailable.

Black★Rock Shooter (2012)
Unlike the OVA, Black★Rock Shooter already had her ★rock Cannon (and her Black Blade) from the beginning of the anime. Additionally, Black★Rock Shooter can materialize the cannon at will, instead of just carrying it around all the time. Despite having unlimited ammunition and firing energy projectiles, the cannon ejects spent shells when in gatling gun form. In Episode 6, the cannon is transformed into the Insane Cannon Lance.

In Episode 8, when Mato Kuroi takes on Black★Rock Shooter's form, she unexpectedly finds the ★rock Cannon embedded in the ground in Black★Rock Shooter's world, after the original cannon had become the Insane Cannon Lance. Insane Black★Rock Shooter tries to get Mato to use the cannon to attack, but Mato just uses it to block Insane Black★Rock Shooter's attacks. When she accidentally stabs Insane Black★Rock Shooter non-fatally with one of the weapon's spikes, Insane Black★Rock Shooter breaks the cannon on her knee, leaving Mato defenseless. However, Mato eventually musters enough power to summon the ★rock Cannon in its three-barrelled gatling gun form, and uses it to fight against the massive firepower of the Insane Cannon Lance.

At the conclusion of the battle, the power of all the "other selves" allows Mato to summon a giant ★rock Cannon, which fires a massive rainbow-coloured beam that annihilates Insane Black★Rock Shooter and the Insane Cannon Lance.

Abilities
★rock Cannon's abilities are seen in the Black★Rock Shooter 2012 Anime and OVA. ★rock Cannon is shown to attack in several different ways so far:
 * It is capable of firing 20 rocks/bullets per second.
 * Can be transformed into a giant blade. (in the OVA)
 * Strong enough to be used as a shield against attacks. However, Insane Black★Rock Shooter can break it by snapping it on her knee (this does not prevent the cannon form being summoned later, suggesting that it has multiple forms or is self-repairing).
 * Can not only shoot rocks/bullets, but also blast slower but more powerful orbs (similar to a cannon-ball). (in the OVA)
 * Can charge certain amounts of energy to unleash a devastating blast. (in the Game)
 * WRS can transform her ★rock cannon along with her wings to form the cannon that fires her Grateful Sunray. (in the Game)
 * Black★Rock Shooter often uses the cannon in close-quarter combat as an effective melee weapon, and physically strikes her enemies with it.
 * Can be transformed into a three-barreled gatling gun. This may have been inspired by one of her skills in the Game. (in Episode 2 of the Anime). In Episode 8 Mato manages to summon this form of the cannon while fighting Insane Black★Rock Shooter. Its firepower is great enough to fight on equal ground with the Insane Cannon Lance's vulcans.
 * Can be transformed into two gatling guns that appeared to be joined together. This upgrade of the Cannon is capable of monstrously high rates of fire. However, Black Rock Shooter is apparently only able to fire them from a fixed position. (in Episode 5 of the Anime)