A patent which credits Masahiro Sakurai as the inventor has alot of details in it as outlined below that covers alot of the unique gaming elements found in the new Kid Icarus: Uprising game, but since this patent was filed by Nintendo last June and published finally on December 29, 2011, it looks like Nintendo has bigger plans for this 'weapon fusing' idea more then just using it once in Kid Icarus.

• patent details a feature for an unspecified shooting game
• patent involves transmission between two systems
• includes a process for fusing pairs of in-game weapons together
• each piece of data in the exchange represents a weapon
• when two systems meet, this weapon data can be fused into a new weapon
• fusion costs coins
• weapons set to transmit cannot be equipped by your character
• a gun and stick can fuse to create "a weapon capable of firing and using magic."
• weapon stats are determined randomly from a pre-specified range
• these include attack power, elemental ability, stamina, shooting range
• fusion is not limited to StreetPassed weapons
• fusion can include two weapons found in treasure chests in single-player play

This is no doubt it is related to Kid Icarus: Uprising. It's just funny to see a patent directly related to this fusion system, I guess Nintendo does not want any other 'gaming' platform to steal their idea.