Fujin (aside from being a lackey with an eyepatch and a penchant for one-word expressions such as RAGE. and SHOCK.) is the Japanese god of wind and a counterpart to Raijin (god of thunder).
He is traditionally depicted with a large sack (from which he dispenses gusts, whirlwinds, etc.) slung over one shoulder, soaring through the heavens atop a mass of clouds.
Being the personification (deification?) of a force associated with destruction and havoc probably shaped his image - hence, he is shown as an oni (a Japanese demon with a penchant for wanton violence).
Now, how do you keep this god from bringing misfortune on you and your household? Simple - place kama (sickles) in front of your home!
The theory goes that Fujin, being more concerned with random property damage than his own safety, doesn`t really watch where he`s going. So an insignificant sickle is to Fujin as a branch is to a bicycle wheel (preventing him from issuing his special Fujin-style misery on your unlucky self).
http://www.kyohaku.go.jp/meihin/kaiga/kinsei/mht70j.htm (Go here for a traditional illustration of Fujin