Looking at his score, I'm going to guess the requirement is lives remaining-related. Will we see 闇 (dark) as well...?
The majority of replays I've seen have at least two or three misses leading up to the stage 5 boss. So my guess is:
- no miss, bees missed = sun
- no miss, all bees = moon/dark/whatever
- no miss, all bees, stupidly high rank - TLB
Either that, or it's a mix of lives, bombs and rank.