User blog comment:Xilinoc/Ch. 651 - The Theatre Suicide SCENE 5/@comment-6073876-20151112152726

so the secret between Kyoraku's double swords is his Zanpakuto, Katen Kyokotsu (Ohana) created another spirit which is Okyou (the child one), therefore it created another short sword, that is why he has two swords even in seal state...

while Ukitake only have one sword in seal state, double in shikai state because his zanpakuto's spirit is twin pisces...