Big Man Japan (大日本人, Dai Nipponjin, lit. 'Great Japanese') is a 2007 Japanese kaiju film written, starring and directed by Hitoshi Matsumoto. Synopsis: An otherwise ordinary Japanese citizen inherits the role protecting Japan against giant monsters by being temporarily grown to approximately 30 meters in height whenever one appears - a not infrequent occurrence.

References:
https://en.wikipedia.org/wiki/Big_Man_Japan