He wasn't sure about that one. So, those six, the one held by Slayer, and the unknown one.
Where was it mentioned that Fuuraiken is broken? And how did we know the names of Senga, Ekitoku and Kojouhaku, was that in those radio dramas and short stories? This pic was made long ago
http://darkside-ky.deviantart.com/art/GGR-Special-OutRage-Guide-188544014