He needed to kill you. He had to fight you. Because he was mind controled by his leader where Kirby his younger brother was an evil person and he was corrupted that himself is a good person and needed to save the world.

"My mission is to defeat my brother to save the world..." He grabbed his sword.

He was a knight who was manipulated into believing if Kirby dies the world gets saved and the world will be at peace.  "Do not fight me brother...you will see defeat." He said.