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"Uwah! I love your food, Blake, give me another sandwich!" Erika ordered, as she extended her open palm to me. She had wolfed down her own sandwich in less than five minutes.
"No, I didn't bought enough for seconds, it was just one for each person." I said to her while rejecting her order.
"Eh?! No way…" She cried.
I don't know why she's such a glutton if she doesn't even have a conventional stomach. Her "Stomach" is a special magical construct her father created inside her body, it takes any food she eats and converts it into pure mana that reaches her Spirit Orb. This process is slow though, and it is helped by special bacteria I detected inside her wooden body.
It is like a "magic stomach" in simple terms. Perhaps she's a glutton because her stomach is way bigger than normal people, so to fill it she wants even more food. Also she does seem to produce waste, as she had told me she goes to the bathroom to do both deeds.
Check "The Protagnist's Sister Is Actually the Strongest"!