You can Set this card from your hand to your Spell & Trap Card Zone as a Spell Card. During your opponent's turn, when this Set card in the Spell & Trap Card Zone is destroyed and sent to your Graveyard: Special Summon it. When this card is Special Summoned during your opponent's turn: Target 1 face-up monster your opponent controls; its ATK/DEF are halved, also negate its effects until the End Phase.
Based on this: http://en.wikipedia.org/wiki/Tonbogiri
For clarification reasons, the ATK/DEF cut is supposed to be permanent (given the flavor of the weapon this is based on); the BTS effect lasts until the End Phase. Originally decided to keep negation permanent, but that would be pushing it.
(Then again, unless you use this on a boss monster; whatever you target with this will either get used for Xyz/Synchro, w/e)
Artwork was done in GIMP; ask if you want it.
Anyway, CnC, fix OCG, etc.
Reps will be given to proper reviews.