An energy gun from the Armored Core series. Typically one of the most powerful weapons in the games it appears in. Generally its shape bears a strong resemblance to the positron cannon from Neon Genesis Evangelion, which predates the first Armored Core game by 2 years.
Its name varies depending on the generation:
KARASAWA-MK2
MWG-KARASAWA
WH04HL-KRSW
Au-L-K29
44-142 KRSV