kinda-double post because i was wrong :p
Nope, turns out that the lower part is the melody, at least for the first phrase. My bad. Cross-checked it with the ending theme and yeah, it came to that conclusion.
Mm in that case I don't think it'll hurt to write single notes! ^^ It's good for contrast, and sixths can mess with the sonority a lot more than someone might hope. So yeah, I'm going to throw in an entirely new idea here - just a single melodic line for the first phrase.