Myrtenaster

Myrtenaster (Mur-ten-es-stur) is Weiss Schnee's weapon of choice. It is a Multi Action Dust Rapier (MADR) that seems to act as a focus or source for Weiss' power.

Description
Myrtenaster is standard-sized for a rapier and primarily silver-gray in color. The hilt forms four prongs that act as a guard around the revolver's chamber-like mechanism in place of the usual basket hilt. Weiss controls this mechanism with her hands, enabling her to change the modes freely.

There are six modes in total, all of which affects Myrtenaster's combat abilities. They are red, light blue, violet, white, yellow and finally, blue. Each mode also seems to have another setting where runes of that color appear on the blade, but only white and red have been seen doing this so far.

Myrtenaster is highly durable, slashing away at the Giant Armor with no visible wear on the blade. Its most prominent ability lies in the revolver-like mechanism held within the hilt, which is color coded with various attributes that activate depending on the mode.

Special Functions
Myrtenaster appears to have two distinct operating modes. The first is where the color-coded energy (presumably energized Dust) acts directly. The second is where the energy is instead fed into the energy glyphs that are the expression of Weiss' Semblance.

The same color selection on the revolver chamber can have radically different results depending on whether it is directly unleashed or channeled through a glyph.

It appears that, as general principles, red is a repulsive effect (harmonizing with the shielding/attack blocking effect seen in the "White" Trailer); blue appears to be a localized gravitational effect, also seen by how it allows Ruby to scale a cliff-face as if she were running along a horizontal surface.

Black appears to be a stasis effect that prevents stored energy from being released. The white glyph appears to be the 'default' type and is possibly the unmodified expression of Weiss' Semblance.

Excluding the revolving hilt feature, while Myrtenaster does have some ranged abilities, it does not, contrary to all of the other protagonists' weapons so far, seem to have any classic "gun" abilities.

Trivia

 * According to early concept art of Weiss and her weapon, it seems that Myrtenaster did not have a basket hilt, but instead possessed a classic gun shape, with the barrel lengthening into the blade and a magazine or grip behind where the Dust was supposedly loaded.
 * Myrtenaster (Myrten Aster) is German for a family of flowers (Myrtle) that are typically found to be white, but can come in a variety of other colors.
 * Unlike many common rapiers, Myrtenaster does not have a knuckle guard, possibly due to the basket hilt. It also does not have a particularly heavy pommel.
 * Myrtenaster can be seen simultaneously as the most static and dynamic of all the weapons in RWBY. Despite Weiss' rapier never changing its physical form, it does have six different Dust compartments that give it numerous abilities, making it quite adaptable to any situation.
 * Whenever Weiss charges with her weapon, a high-pitched screech can be heard.