The mangaka mentioned something about Mii-chan's model and her grave in a
tweet, so make of that what you will.
For those who don't know Japanese but are curious about the linked tweet, the mangaka was responding to another person's tweet that said something like this:
"This author talked on Twitter as if it were a story about someone they knew, so naturally, everyone thought it was something that happened in real life.
But then, when it was announced that it would be released on MagaPoke, she started saying things like, 'I don’t know where you got that information.'
And as soon as it became a serialized work, she deleted everything from Twitter. Honestly, it feels pretty annoying."
The mangaka addressed this by clarifying that while her friend served as a model for Mii-chan, this doesn’t mean the story is entirely based on real-life events. In fact, she intentionally embellished parts of the story to prevent readers from identifying actual people. She added that if she hadn’t done so, Mii-chan’s grave might have ended up like the "Beast’s Lair" (野獣邸), whatever that might be.
This seems to suggest that the person Mii-chan is based on has passed away. However, the circumstances of her death could be very different from what is depicted in the fictional story. I’m not entirely sure what the "Beast’s Lair" refers to, but it might imply the mangaka was concerned about fans identifying the real Mii-chan and disrespecting her grave.
The mangaka also explained that she deleted her earlier version of the story from Twitter and Kindle because she felt she was being exploited (though it’s unclear what she means by this). She mentioned wanting to finish the story on Twitter but ultimately decided against it because, as she put it, she would have become "useless" if she did. This likely means she was concerned that completing the story on Twitter would render her redundant or devalue her serialized manga, as readers might not feel the need to buy it if the story was already freely available online.