The Beam Katana is the main weapon that Travis wields in the game No More Heroes for the Wii. It is basically a long, sword-like weapon that sends an electric charge through it, making it dangerous. It is controlled by swinging the Wii Remote and Nunchuck back and forth, as if you were really fighting the in game enemies. There are various techniques that he can perform with the Beam Katana, including a lock-on power and blocking moves.
There are rumors that the Beam Katana is based off a Lightsaber from Star Wars, unsurprisingly.