AFAIK, Tessen were blunt weapons.
They were basically small clubs that could be unfolded to signal the troops, act as small shields or to aid oneself floating.
I think they could have spikes at the ends and therefore act as stabbing weapons, but they were mainly used to parry and/or disarm your opponent, as well as to beat, strangle him, break his arms or help you hold him in a lock.
Of course in manga/anime/videogames you'll find characters wielding war fans of any size and sort (be it spiked, bladed, magical, giant,...), so I guess anything is fine unless you're running a strictly historical campaign.