they're using the bro forceIt's not explained how Serafune and Konishiki (the brother) are able to communicate with each other telepathically.
The first chapter also had the MC’s form when turned into an octopus. Wouldn’t read too much into it yet.Waitaminute...
The other demi-humans in the beginning of the first chapter
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Every other person on that page had some visible abnormality, she was the only one without one, it wouldn't make much sense if she was not demi-human. There also very likely the same character since the shirt she's wearing is also extremely similar as well. Not only does the collar look the same, but both have the same type of stripe as well. Also, there's even a panel where you could see that the gaps in her hair are in the same place as the one in the colored panel.The first chapter also had the MC’s form when turned into an octopus. Wouldn’t read too much into it yet.
Then again, it could turn out like another series where almost everything was laid bare from the get-go.