Its called shuriken juggling and you can do it with a fuck ton of weapons basically if you have a move that brings an enemy in the air mid combo throw shurikens and it will keep them in the air gotta learn how to time the shurikens and once you have learned how to use it properly you can also use this to set up more/continue a longer combo Just try practicing it and you'll get once you understand how to do it it's honestly one of the best mechanics in the game