Gattai is the English transliteration of the Japanese word 合体, which means “union” or “fused.” Like the giant robot from my childhood, Voltes V. In Sudoku, it describes the combination of multiple grids into a single larger puzzles.
Yojimbo
It may seem like a lot of constraints, but it's a Samurai Sudoku, so you should only have deal with one or two at a time.