Type: Plot Device, Deus Ex Machina
What made it popular: Various battle-shounens, Japanese mythology and folklore
Cliche Level: Extremely High
Where can you find it: Typically action/adventure anime, Shounen and Seinen alike, but you can also find it in drama, horror and thriller genres.
Description: The protagonist/or another main character is in trouble, surrounded by enemies and he is pretty much about to die and has no chance of survival whatsoever, how is the writer going to pull the character out of the mess? Easy just activate the characters hidden power that was there all along even though it was never mentioned or foreshadowed previously and pull the character out of the mess. This power can range from transforming into a giant naked guy, awakening your clans power, a curse, 2nd personality or letting the demon inside you get control as well as the many other ways writers have come up with during the years. Either way, they usually look like this.
Whatever method is used, the result is the same. The main character overcomes his adversaries and lives to fight another day. There are only a handful anime that actually manage to avert this trope or use Hidden Power with actual foreshadowing. The usage of the Hidden Power is usually accompanied by glowing/or dull eyes, sudden auras, intense change in music, hair colour change or other similar visual transformations.
Why it’s Bad: As I already said most of the time there is absolutely no foreshadowing of this hidden power or previous implications of it’s existence, meaning that the author is basically pulling it out of his ass whenever he made a mess and can’t pull out the character from the trouble without using this or another deus ex machina.