XnView Software

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Your example is something I do very often, although not with pokemon characters .
It is handled by child categories - make pokemon the parent and then child categories for all pokemon characters.
You have an option in xnviewMP to automatically select parent categories.

Of course, this only represents a subset of possibilities that a more generalised scheme would offer, but it does exist already, and does take care of most situations I need.

The category heirarchy also makes navigation much easier as the numbers of categories build up.