Thank you for the suggestion! My idea with the light and dark theme is mainly to establish that connection with the player or the player to establish a connection with the theme of the game. I don't know if this is to harsh of a topic on here but like some other games that explore mental health, I to want to do this. As a person who suffered from depression in the past, the light and dark theme is something that I want to really reflect in the game. The dark is loneliness, sadness, despair, and fear while the light is comfort, joy, faith, and courage.
Sorry if my explanation is not well thought but that's where I want to head with this theme. I went with the good will fight bad trope because hope (light) is like your mental warrior trying to defend and fight of against your dark moments in life, at least that's how I see it. Now in terms of the bird protagonist or bird theme, that was something that I just picked on since birds symbolize new beginnings, hope, freedom, prosperity, peace, and joy.