Yes, you're supposed to get him when you mate an Otokitchi (Matchmaker) with Ojitchi (Old Man). And to get them, you have to let an adult male and an adult female evolve into old timers...that's why they're not very common.
Get a Masktchi, preferably male and take very good care of him and don't mate him with any tamagotchi and eventually he supposedly takes his mask off and out pops Ojaritchi.
Forgot to mention. This is on V1, on V2 the secret character is to be found out though tamergotchee got Nazotchi as an adult but you never know, maybe it isn't the secret character...