Further ai investigating. If an enemy would do the same amount of damage to two units (eg: takumi vs. deciding whether to go after one of two flying units, both with the same def and spd), then it seeeems to go after the closer one. Or at least, the one that was the closest initially at the beginning of the match. Once it decides to target that unit, it sticks to targetting that unit for the rest of the match. Or at least it seeeems to. There's one instance or so where a takumi ended up deciding to go after the one that was closest from turn 1 for the rest of the match, so maybe it just picks one of the two at random and then sticks to going after that one for the rest of the match.
e: I deleted the 2nd paragraph since I was mistaken, but if anyone read it, ignore what I wrote, I was going insane after all.