There is no hidden Aya path. One might have been in planning at some point very early in the game’s development, but that’s pure conjecture; it’s impossible to know without getting word straight from the developers at Ruf, and they aren’t talking.
Considering that they went to the trouble of arranging a non-blood-related scenario and providing at least some romantic interest between the protagonist and her (not to mention giving Aya her own block of scenes in the scene replay extras section) it does seem suspicious, but there’s really no way to know.
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