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DDLC borrowed a lot from YOU and ME and HER: A Love Story (Kimi to Kanojo to Kanojo no Koi), which I consider generally superior to DDLC. I say this not to diminish DDLC, which is excellent, but as a plug for anyone who enjoyed DDLC and wants more mind warping content like that.

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I believe Dan Salvato, the creator of DDLC, said he wasn't aware of YOU and ME and HER until late in development.

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Convergent evolution. It’s probably just an amazing and fortuitous coincidence. They look similar but have completely different internal structure, like a bug that pretends to be a leaf. I can’t go any further without spoilers, so I won’t.

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There might be a slim evolutionary thread between them, actually. DDLC made a reference to a certain Gravity Falls episode which has a similar premise by releasing exactly 3 years later, and that one could have been inspired by the then recent release of Totono during production.

But I agree it's convergence for the most part, it's not that hard to come up with that premise even if it hasn't been too common.