It appears that there will be three different ways that folks can enter for their chance at the Nano. For one, there looks to be a specific difficulty setting that will apply to this giveaway, meaning that players who partake in the game while in this difficulty setting can upload their high score for entry. Second, players can collect certain in-game prizes (or tokens, we're assuming). Third, there's an online survey that can be filled out.
Seems fairly easy to us, and there will be a total of 15 Nanos up for grabs. The contest period began on March 21st and ends on April 16th. Again, we're not certain this applies to folks outside of Japan, so keep that in mind.
Gallery: Ninja Gaiden Dragon Sword