Wait, didn't the previous chapters explain how Hourai beings can't go insane?
Based upon the chemical makeup in the brain it would technically be impossible for a Hourai to go insane as their bodies constantly regenerate, thus returning their brain functions back to their original settings.
But even so the psychological damage my just be too great even for someone who can effectively hit the reset button on their brain. Also 'sanity' and 'insanity' are based upon a person's current understanding of the world and how they interpret it. Since the 'world' is now the endless expanse of space she must expanded her understanding of it and unfortunately a human simply doesn't have that level of processing power, immortal or not.
Mokou's relapsing into her old Insanity phase back when she was a fresh Hourai Immortal. She'll get better once she gets bored with being insane. Again.
Since then, she has been drifting alone in space for over a hundred years...Right now, Mokou is on the verge of going insane.Breathing and talking is impossible, yet even so, she still cannot die.Temperature is -270 degrees Celsius, an eternal night without daylight,Here, in outer space, a hundred years is much more terrible compared to a hundred years spent on Earth...!!!Fuck...!!!Shit...!