Great topic! The first day I didn't even touch the DAW, I just looked at the theme and wrote down notes about what I was seeing and what kind of story could be made from it, determining that I wanted an intro (the girl's theme), a conflict, a theme for the ancestor, and a resolution. Then the second day I decided the orchestration, which was a lot of just looking into how classical Thai music is orchestrated and what instruments are used so I could try and incorporate that. Then once I started, I knew I wanted to highlight the resolution with the girl acting as the melody and the ancestor as the counter melody, so I sort of wrote that as its own thing so I would have their melodies ahead of time.
After that, I just sort of went section by section, voice by voice, using a melody-first take. With this, if I didn't already have a melody in mind, I would just sort of play around on the keyboard until something sounded fitting. Then adding harmony was a mix of creating chords that move according to music theory and just making chords by what sounded good due to time constraints.