I'm currently running 2B>5C>2C as a punish for Koromaru. The "combo" takes off most of his health, about 90% (I couldn't find anything better, I was hoping for 100% so tell me if you guys find one). The 2B>5C cancel should be immediate (as if you were trying to get 1 hit of 2B) so that 2C doesn't whiff. 2C will also whiff if you hit Koro in the air.
Ken players will generally cover their dog so you probably wont get to do this very often, but if you ever see they're giving you time and space after 2C or something you can punish Koro. I've had Ken players just sit fullscreen and mash Koro 2C sometimes, so having a good punish will help discourage that. You can backdash on 2C (in the combo) for safety if you see Ken going in while you're bopping the dog, but beware of charge thrust if he's in range for it. It's also helpful that hitting Koro has very little hitstop, you can get your damage pretty quickly.