I've played a lot of games about mental health, where you play as someone that has to fight the embodiment of depression/psychosis/anxiety/etc. (GRIS, Celeste, Hellblade, etc)

Never once have I played a game where you play as the mental illness.

It's a disturbing kind of power trip. You realize that this girl is in your hands, but even you are limited in what you can affect. Your cruelty and/or benevolence is still constrained by whatever the girl is capable of thinking or experiencing. Even as a life debilitating condition, you are not all powerful. Easily one of the most thematically intriguing games I have played.

Highly recommend, it'll take you 20 minutes to finish and it's a mere $1 USD at full price.