You haven't had true OC hours until you start thinking of theme songs and anime style openings.
Splitting Image has two I'm always thinking about, from the Persona series - usually my current works have whatever game is really influential to them, Road Less Taken from Persona Q2 and Pursuing My True Self from Persona 4. They're... also anime openings but sometimes you just have to be self indulgent.
As for general "mood" themes, I'd say Surviving Exile from Pyre. Aeolia is a cheerful world with much to explore, but still with a sad undertone as people die frequently and the islands just stop like a story with no ending.