Kaito is the first born son of the Mizuno family (he has two older sisters, but females technically can't become head of the Mizuno family). Not much is known about how he grew up except few things. Kaito was raised on an imperial world and also went to imperial schools for a short time, but when he was just nine years old, he left school and was educated by a private teacher together with his twin sister Rin. It is not much known to public about anyone in the Mizuno family. The Mizuno family existed quite peacefully for over 700 years already and not much information about it members leaked out during this time and this didn't change until Kaito became an adult.