It's called the Vár, and it's a customized combination of anti-materiel machine gun and fencer sword. It can be used only by its maker, Imca, a Darcsen squaddie now known as "No. 01". Yeah, when you see someone with a weapon that big, you kinda have to assign her the number one. Not that that's a problem, once you see her use it. Imca keeps the weapon no matter what class you change her into, and her "Open Fire" special ability allows her to target all enemies on the screen. If you're overly concerned about "realism", I'd like to point out that nearly every "white person" in the Valkyria Chronicles world is descended from a bunch of vikings whose WMDs took the form of silver women that are also on fire.
Check out the trailer below, as well as some of the fun retailer-specific extras that will accompany the Japanese launch in the gallery. We probably won't get them, as they're mostly telephone cards with illustrations by character designer Raita Honjou. If you're overly concerned about the proliferation of boobs, you should see some of Honjou's less, er, work-safe, pre-Sega work. Mmmm.
Valkyria Chronicles 3: Imca in the spotlight [Andriasang]