'And I'm Here' by Kim Kyung Hee
It's an OST from Goblin and whenever I hear it I get bombarded with my own emotions and that of the drama. It's also all in English, so that helps me get a deep emotional connection.
'Promise' by EXO
Chanyeol's rap in Promise makes me emotional just because how raw and honest it sounds. You can hear his pain in the urgency and roughness of the verses.