In Zeorymer, Masato seemingly has two personalities, his normal naive demeanor, and a homicidal demeanor. The TRIGGER for his personality to switch is when he pilots Zeorymer, which unlocks the personality and memories of Masaki, the man who created him and Zeorymer.
Masato is a clone of Masaki, genetically engineered to be completely rewritten as Masaki when he comes of age and pilots Zeorymer. However, Masaki's personality cannot take full control outside of piloting, and thus Masato's personality still lives when he is not piloting. (except for one instance, but Masato snaps out of Masaki mode after killing 3 of the Hau Dragons at once, and he actually ends up in the middle, and no longer is Masato nor Masaki.)