>>132872480I'll explain it in completely in simple terms so that even someone like you could understand.
When the anime staff were writing a filler arc, they decided on a plot involving the zanpakutou spirits of the cast. However, when they did this, they didn't want to contradict canon, so they asked Kubo to design the characters for them.
So, based on his plans for his cast, Kubo gave them Zanpakutou spirit designs for everyone, Kyoraku included. It's not as if Kubo made all of these designs for the sole purpose of being used in the filler arc and never seen again - it was never for a moment supposed to be that way.
Now, in this fight, Kubo decided that he wanted Kyoraku's Zanpakutou spirit to appear. Naturally, he used the design he made for her back in the Zanpakutou filler. This shouldn't be surprising. If, by chance, that filler arc never happened and he didn't make the design back then, he simply would have went through the same process and designed something similar.
There is no reason that Kubo should neglect to use a design he made just because a filler arc it appeared in was bad.
