I don't know if it's called "petitichi" but there is a petite family on the v5. I think you get that if you take REALLY bad care of your tamas. but, I don't know all the details.
Petitechi is a character in the petite family.To get it you must neglect feeding your character but keep it happy.There are specific items you can give them to make them change back.
Petitichi is one of the characters in the Petite Family, to get it, you just have to underfeed your tamagotchis and automatically it might turn into a Petitchi and then it can get married with another Petitchi, which makes the Petite Family.