What is 'gattai'?
Popularized by Japanese giant robot type shows, the term literally refers to the act of merging two separate entities. It is often interchangeable with similar terms such as fusion, combination, joining, etc.
In both of these situations (Rangers and Voltron), the feat of multiple bodies becoming one can be representative of Foucault’s idea of bio-power. When the five, uniform Rangers combine their efforts and bodies for the greater good and to become an overpowering mecha, they can accomplish something greater and become a part of something more powerful. They are usually only able to combine when they are all in "sync." This usually means that they are all dedicated to fighting a common evil, while trying to preserve the good.