As an archer, Kai's tactics largely revolve around kiting and long-ranged assaults, so keeping one's distance is essential in most fights. Kai can transform his bow into a long or short variant, with the long doing more powerful (but slower) attacks and the short one pew-pewing much quicker at closer range. He can also unleash an attack that hits multiple targets at once, making him ideal for some burst AoE damage.
One of Kai's more unique skills is the ability to place a marker on the battlefield and then quickly grapple his way back to it on a moment's notice. While he's traveling back to his marker, he's immune to all damage, making this a strategic move for pitched fights.
Kai is coming to Mabinogi Heroes in Korea tomorrow, although it will be some time before he lands in the States or Europe.
[Thanks to Justatip for the tip!]