UPDATE: The official Hyrule Warriors Twitter account has stated that the game will not support cooperative multiplayer over the internet; however, this does not rule out competitive online multiplayer.
According to the online interactions section of the Hyrule Warriors listing on Nintendo’s website, the title appears to have some sort of online play.
The online interactions box lists “purchase of additional content, automatic posting of play status to Miiverse, and play special battle in adventure mode” as Hyrule Warriors‘ online features; the first part is obviously DLC, and the second part is Miiverse integration. The third part, however, seems to suggest that there will be some sort of “special battle” mode in the adventure mode; we’ve already seen that local multiplayer is available, so maybe you can also play cooperatively with a friend over the internet? Or maybe you can battle against armies commanded by other players around the globe?
What kind of online multiplayer would you like to see in Hyrule Warriors?
オンラインによる協力プレイは対応していません。ご注意下さい。Game Padを使ったオフラインでの協力プレイは出来ますよ！"@_orngrg_: ゼルダ無双ってオンラインできるのかな？？？？？？"
— 「ゼルダ無双」公式 (@zelda_musou) July 31, 2014