Great question! (And I'm glad you enjoyed the demo!)
Yuu is actually heavily based off of myself. I'm not sure if I did this intentionally or not, it just sort of happened as I wrote the game. And a lot of the people who know me in real life picked that up right away, hahaha.
Now, it's important to note that Yuu is definitely an exaggerated version for the purpose of entertainment, but I still feel like he heavily embodies what [I believe] it means to be clinically/chronically depressed and thanatophobic, among other unnamed illnesses. The 'nightmare' scenes (Which there will be more of) are things I only write when I can feel myself "slipping."
Each character in Nothing is Beautiful contains a different piece of me, so it's great to see all of them being received so well.
Thanks again for commenting and I hope you enjoy the final version when it comes out!