Woow that's pretty cool...
Yeah if I had a zanpakto or be able to create one... i guesse the name would be "Toutotsu ojike" which means sudden fear. Ablities would have to be obviously causing the person to keep on remembering what that person's ultimate fear is or bad memory, consequently making them unable to fight right.
Bankai would be making that person be trapped in his/her worst, most horrifying memory.
I think it would be kinda cruel and kinda freaking if the personality would be very cheerful and childish except for the fact the it would only say things in a dark manner. Uuhh chills n_n