Spoilers.
Theme: I don't know if i saw it.
Story: Well done. This feels like it could be a proper short story, ready for submission to a magazine with some additional tinkering and adjustments. I think we don't have enough time for the ending to pay off-- either we need to get to the relationship quicker, or we need more time regarding the relationship to make the "love" resonate further.
Still, I felt like this had some tight prose, and you understood the overall pacing and scope needed for a work this short, which I very much appreciated as someone that writes a lot of flash fiction (shout out to apex who still hasn't let me win a month yet :P)
Presentation: The song you chose fit the mood, but you went a bit spartan overall. It fit the needs, but you had like "hovering sprite" syndrome. I also don't know if I got "bunker" from that stairwell and other elements, barring like rich person bunker AND/OR Life is Strange murder pit (the dark room.)
Creativity: I appreciate your tale, a quick poignant exploration of being haunted and death.
Overall thoughts: Great attempt, although my only caveat is I don't know if it fully cared about the form of the medium, even if your prose was doing great work for me in the brief window of time.