Killua likes China quite a bit. It helps that he reminds Kil of a close friend. Though it did help that China had the guts to talk to Killua, when the brat was still raging over his brother and sort of calm him down. That earned China a lot of respect from the brat.

He see China as someone that is knowledgeable and wise yet still down to earth enough to tease. He'll be teasing the guy more often but it will be friendly teasing as friendly as Killua can convey.

Oh yeah if he ever figures out who hurt China he wouldn't hesitate to make the culprits life a living hell.