For a second there thought Rika got shrunk/lolification by a mad scientist/wizard, but it's just a wish fulfillment fantasy not A fantasy story.
Guess Rika father, Ishida, ran away from batshit insane mom, eh?
At least he could call or take his daughter away, Aoi is more on the extrovert side instead of timid-introvert-anexity as Rika... proper parenting makes wonders it seems...