GSGW pt 2 ending spoilers
Sleep as a concept in gsgw.
Think about it: From his first day in the DER world, Kim Soleum has not been getting good sleep. At first they were caused by nightmares of what could happen to him, but when he becomes 130666 he loses the ability to sleep entirely.
Sleep, of course, is a time for restoration, and without it people would undoubtedly go insane (and I think that the lack of sleep is also a reason why kse slowly gets more and more emotionally unstable beyond, of course, the circumstances). When he is more darkness than human, i.e in Braun's Talkshow, I'm pretty sure he doesn't sleep as well, perhaps showing how inhuman he has become.
Then, as 130666, when the ability to sleep is ripped from him, it not only shows that him is no longer human (or has the rights to be one) but also shows how he is going to be treated like a tool, pushed to his limits and then some more.
And what does he do when he gets home? Take a nice fat nap (real).