energy sword
レーザーブレード ビームサーベル ビームソード レーザーソード
A sword with a blade made of some sort of energy instead of a physical blade.
The best-known example is the Star Wars lightsaber, but energy swords are also very common in science fiction themed anime and manga.
Characters such as Kuwabara Kazuma from Yu Yu Hakusho and Vegetto from Dragon Ball Z are known for having energy sword attacks.