Someone in Zhihu made this answer:
1, the angle is set by people.
Because the rabbit is a princess (although other soldiers are also princesses ... especially Minako, the protagonist of Mariner V).
It's not that other planets can't be princesses, but in the existing legend, the moon is the most fairy tale atmosphere among the nine (or eight) planets (especially in the East), and it is also the planet that people are most familiar with.
For example, in the previous play, Minako was the leading role. Although Venus, as an independent princess and warrior, has no problem in artistic conception (love and beauty), as a leading princess, Venus is not as good as the moon in overall artistic conception and atmosphere.
2. CP of men and women
In the solar system, only the earth and the moon have the most CP sense. Therefore, the male and female hosts are tuxedo masks and beautiful girl warriors. At first, Xiao Wei was the protector of the rabbit. Finally, the rabbit was the princess of the moon, which could protect Xiao Wei, all her partners and the whole planet (the world).
This is related to the theme of the work.
"Beautiful? Guardian? Sailor? Moon ",this is the official English translation of the title of the work. Please note that the English word "guardian" is used here instead of the soldier.