I take it you haven't got the weapon, in which case you'd have realized it does have its uses, it's very easy to get, and it shows you the location of a free health and ninpo refill if you're in the area.
Actually, no, I won't report that as trolling. You're a GS user, that's punishment enough. ~Nemephosis
Oh yeah!In Very Hard and above there are powered Black Spider Ninjas(The purple ones)that use them and they knock you off the air EVERY time.Take the weapon.Well,Ayane DID say it is a Legendary weapon.It is useful.
You can use the Windmill Shuriken to spam hits on those awful grim sorcerers that fly around holding scythes. Before I figured out their attack style, I just hopped around and chucked the Windmill at them until they were toast.
In the Mission with Ishtaros accompanied by those dudes, every hit counts.