[SPOILERS]
For me, after getting all the endings I thought for sure this game has to be about depression. How you try to get rid of it but it's always in the back of your head. You try so hard to push away but it tells you that you need it to survive. But the harder you push away the better it gets. Although you may just want to surrender and give in to the fight if you keep going it's bound to get better. No one else can see the fight, just as her friend couldn't see the man/woman in the picture, but our brain convinced us that it's been there for years.
I think this game overall is just amazing. In fact, all your games are eye opening and make me reflect with every ending.