The 2 secret characters obtainable on the Tama-Go are Grippatchi and Oyajitchi. When you marry two senior Tama-Gos by connection, they will have either a boy or a girl baby. When the parent leaves, an hour after the baby wakes up, it will evolve into the secret character. If it is a baby boy, it will become Oyajitchi. A baby girl will become Grippatchi (AKA Miss Perfect in Tamagotchi Anime). I currently have two Oyajitchi. Unfortunately, as was said earlier, Nazotchi, the shopkeeper is not obtainable in this version. In some others, he/she/it is obtainable through debugging.
Hope this helped!