Fruit of Wisdom

In legends such as in Judeo-Christian texts, the "Fruit of Wisdom" is the source of giving knowledge to mankind, while in actuality it was a special fruit that increased the mental capacities of anyone who ate it, allowing for them to become a genius. The fruit appears similar to a bunch of grapes and grows only as one of several bunches from a certain tree, which must be tracked down for the right one to be selected. Unfortunately the brains gained from eating the fruit only last a short period of time, and it must continued to be consumed for its effectiveness to last, with it's power going away once the last piece has been consumed and it's effect worn off.

The Boukengers and Dark Shadow both track down the fruit, which ends up in the hands of Akutagami, a Tsukumogami idiot created by an accident of random junk being spilled during Gekkou's creation ceremony. Due to appearing to fail in it's mission, Akutagami is punished with no dinner, which allows for it to instead eat the fruit, instantly increasing it's mental capacities and turning it into a genius no longer interested in working for Dark Shadow. Akutagami tries to join SGS due to becoming slightly friendly with Eiji during their first encounter, but their fears of working with a Tsukumogami and their own desire for getting the fruit back makes it realize that humanity is just as much a problem, making it go on a rampage to disable humans by destroying power plants and raining junk from the sky. Ultimately Akutagami runs out of the fruit just for Yaiba to strike it down for betraying the Dark Shadow, yet the junk Tsukumogami prepared one final act to save itself while it was a genius: using a special charm prepared and given to Eiji to stop it in it's giant form so it could appear to die yet allow for it to shrink back down and go into hiding even though it no longer possesses any further genius.