>>2035854Haato and Haachama were sisters
After an accident, One of the sisters died. But the other couldn't accept the loss so she created an imaginary version of her sister. Unfortunately, due to this trauma happening at such a young age, the mental maturity of Haachama is that of when she was young, since that was the last memory Haato had of Haachama before death
Cut to the present, the delusion has turned into a borderline alternate personality that Haato has no control over and takes over the host body at times.
The real twist is that the personality is actually Haachama's soul haunting Haato and trying to possess her sister so she can Live Again
Coexist is both spirits coexisting with one another. The head cutting was a metaphor for Haachama completely taking over, by getting rid of Haato completely, removing all thoughts and the mind and replacing it with Haachama's spirit
At least, that's what I think the whole plot was
