From what I could dig up, this instance is much the same as the Zanpakutou from Bleach - you would apply for it in Items, as the Characters staffer suggested doing.
Even with a different form, it is still a weapon and Items is the best category for it to be listed.
If you still think it should be cross-listed into Characters, I'd suggest sending in a contact form, and I will discuss it with the appropriate staffers. ^^