#golden crystal

Female Senshi

The reason all senshi are female- and why male starseed carriers (Mamoru) are weaker fighters- is simple enough. (Meaning: bear with me.)

A senshi holds the responsibility for her planet and dies when separated from her starseed. A senshi capable of using two starseeds would not only be responsible for two planets, but would have access to twice the power. In this way, Chibiusa is an anomaly because she can tap into both the power of the Earth and of the Moon.

Originally, when there were certain ‘rules’ being set for senshi, it was decided they should all be one one gender so there would be no breeding between them with the end result of, say, a senshi with the power of twenty planets. (Hard name to get one’s mouth around as well. [Which could, when extended, explain Sailor ‘Cosmos’ as a possible amalgamation of many planets?] Anyway…)

The reason females were decided upon was because senshi were descendants of the royal family of their planet, usually in a patriarchal system. Crown princes were too important and busy being future kings, although occasionally (in the instance of Endymion) a starseed would be passed to the wrong person. This left some less-important princess or another to be trained as a warrior to serve and protect her planet.

In the case of one such as Mamoru, the powers of his starseed manifested in a lesser, weaker way so as to be unassuming and not attract much attention; again, to avoid him being prey to some senshi who decided she wanted a daughter twice as strong as herself. Which brings to point another reason the people of the Moon couldn’t marry those from Earth- everyone knew Earth was missing a senshi so until she was reborn as a girl, the Earth would have been ‘quarantined’ to prevent senshi cross-breeding (and related mutations; albinoism, slow growth, or dwarfism for example).

So Chibiusa is basically what the powers-that-were didn’t want to happen, but oh-well-for-them-anyway.

…And we all know she dyes her hair.

This headcanon elaborates on two ideas; Chibi-Usa’s problem with aging + power, and the ever-elusive Sailor Cosmos.

Chibi-Usa was born with control over both the Silver and Golden Crystals. The reason she was permanently stunted and weak was because her body needed to choose which Crystal to “inherit” before she could progress to puberty, and was in a stalemate trying to choose which one. When Chibi-Usa chose the Silver Crystal for herself, she started to age, and the Golden Crystal became dormant inside her.

However, in the distant future, beyond Crystal Tokyo when she has become the new Queen and Sailor Moon, a villain much like Galaxia appears and takes her Silver Crystal. It is destroyed and sent to the Galaxy Cauldron to repair and be reborn.
Normally Chibi-Usa would die in such a situation. But because she had two Star Seeds, the Golden Crystal shifted forward into the dominant position, replacing the Silver Crystal.

But the Silver Crystal still went to the Galaxy Cauldron and still needed to be reborn. With its original host living, essentially, with a replacement Star Seed, it had nowhere to go, and so drifted off into the ether; to the distant future? To an alternate universe? That’s uncertain. But being so powerful it eventually gained a human form, similar to the Crystal’s original host - Queen Serenity - and with only a vague personality that was a diluted shadow of hers.
Sailor Cosmos is not a person. She is the personification of the Silver Crystal, and that is why she returned to that past; not because of Usagi, but her Crystal.
Meeting Usagi gave her humanity.