[There's some kind of heavy Japanese pop culture reference here that I'm completely unfamiliar with. Sendatchi is a nod to another Japanese entertainer, Senda Mitsuo who has apparently coined a catch phrase of sorts, "naha naha" and as such, all Sendatchi ever says is "naha naha! Senda! wonderful!"]
Sendatchi is quite a difficult character to get. So, if you do get Sendatchi and get to show it to Senda Mitsuo, he'll probably be very happy and give you a present. But, it's pretty embarassing to use the care methods required to get Sendatchi.