In Co-op mode, Kai's REC stat is increased from 5 to 6, due to his base ATK of +1. Kai's passive does not change.
Kai's Hyper, Protagonist's Privilege, has a different effect in Co-op. When used, the player will always attack first in battle and the opposing unit will skip their attack roll. This effect lasts for 3 chapters. (In all other aspects, this Hyper functions similarly to its Normal mode counterpart.)
Kai's passive and Hyper are unchanged in Bounty Hunt mode.
Kai's base stats give him 30 starting stars and a markup of +25% at shops.