Kao ni Denai Kashiwada-san to Kao ni Deru Oota-kun + - Vol. 1 Ch. 10 - Kashiwada-san and Obon

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I thought Natsuka could be one of two things, and one of those was Kashiwada's grandma, which obviously isn't the case anymore.
So maybe it's the second thing I thought; she's Kashiwada and Oota's future child???
Sounds weird but that's what my brain guessed.