I loved how they always use the same background music for the mysterious scenes!

I think it's intended by the directors themselves that these scenes have the same background music, so they bring you on the same train of feelings!

First MV, is the scene just before their first kiss + the ending scene from episode 15.
https://www.youtube.com/watch?v=77il5vSBNzE

Second MV is , their first encounter + the ending from episode 15.
https://www.youtube.com/watch?v=IgLL_kasePU