Did the silver crystal (cosmos starseed) jump ship from Queen Serenity to Princess Serentiy when QS died? Does it have something to do with a compatible host?
I'm going to assume you mean in my hcs because if you're asking canonically, I genuinely have no clue how the "passing of star seeds" works.
The way I see it, the Silver Crystal is a truly unique star seed in many ways, one those ways includes the way it's passed down from host to host.
I've briefly explained in the past how star seeds work in my hcs.
Super brief tldr: basically star seeds are the initial "pure" stage of a Sailor Senshi. Sailor Senshis themselves are NOT a species of aliens given no commonality of location, origin or biological background is required to birth one. Any species of alien CAN be a Senshi given they fit within certain criteria.
By those standards, the closest "real life species" that I can compare star seeds to are parasites. Stick with me, they're parasites because they need a compatible host to "nest in" and birth a Senshi. It is a kind of symbiotic relationship where the seed technically benefits more than the host itself, commensalism.
For 99.9% of all Sailor Senshi, the way star seeds jump form host to host is "random". It is not through birthing offspring; Sailor Jupiter can give birth to children, those children will NOT be the next Sailor Jupiter.(it COULD technically happen but the chances would need to be one in a billion if not much rarer. Like, Jupiter would literally need to die DURING childbirth and also there would need to be no other compatible host nearby for the seed to jump to and the child would need to fit exactly the right to fit the right criteria needed for Sailor Jupiter specifically. You get the jest, it is an abnormality.)
Random in the sense that, once a previous host is about to pass away or has already passed, the seed will lie dormant within their body and seek the next closest compatible host. (The host would have been born regardless) Each seed has general criteria (like being a female) and more specific criteria tailored to their Senshi's needs specifically, being biological traits or ones born from their backgrounds (like how the seed for Jupiter needs someone with a larger physical build or even how the Mars needs a host born into an environment where they're more likely to be exposed/involved with elements of prayer, faith and clairvoyance).
It's not a perfect system, perfect matches are a rare luxury, not an assurance; all a good match does is increase the chances of survival of the host. The better the fit between the host and the criteria (which is shaped around the identity/powers of the given Senshi), the stronger the Senshi. The stronger the Senshi, the lower are the chances of them getting killed and for the seed to have to repeat the process after too short a time too frequently (seeds want to stay within a host as LONG as possible, they want the host to adapt and "turn into" a fully adult Senshi to use its powers. Seeds have TOO much power. If they don't find a suitable host that can regularly exercise the overflow of power a seed provides or have to switch the host too frequently given a Senshi is not fully able to exercise their powers till adulthood, the seed will start to crack and will eventually break under the immense pressure of its own core. The explosion of matter and energy resulting from the breaking of even a small star seed can be powerful enough to create its own black hole and will surely destroy the planet the host was residing in, along with other nearby planets and celestial bodies.
All of that is to lay down the rules of how star seeds normally work, the Silver Crystal aka Sailor Cosmos' star seed is NOT a regular star seed.
The way the Silver Crystal passes down from host to host IS through preproduction. The current holder of the Silver Crystal needs to give birth to the new host (asexually or sexually) just because the criteria HAS to be perfect. It literally creates itself a new "perfect" host.
The Silver Crystal cannot and will not take any chances with any of its hosts and it hold enough power on the world and reality around it to make sure risks are minimal. I'm ALWAYS a big fan of the idea that the Silver Crystal (I'll shorten to SC) holds a low level of sentience and intelligence, all seeds do but the SC is the only one truly able to exercise and manifest it into reality. It has the power to shape reality at will, though this power is fairly limited when not directly exercised by the host, which will never happen because.. come on, if you had the power to do anything, would you trust even the person closest to you to not do some bullshit with it?! Even by accident. Even the SC has universal rules it has to abide by.
Another reason the SC is the only seed that's able to be passed down through direct offspring comes from its ability to physically exist outside of its host's body WITHOUT killing the host. All other seeds, if removed, will kill the host immediately. (that's what makes Galaxia so threatening and dangerous, she's the only Senshi able to immediately remove a seed from the host and once the two are separate there's no backsies, the current Senshi is super dead. A seed can live and exist for a while without a host, a host cannot survive without the seed once it's fully nested.)
Queen Serenity gave birth to Princess Serenity, but she was still the only one to hold and exercise the powers of the SC well into adolescence (which is typically when a Senshi's identity first starts to awaken). Although say if *somehow* the SC got destroyed there and then (not counting the massive implosion that would cause. If the SC got destroyed the impact of it would be on a universal scale, like big bang lvl) BOTH Queen and Princess Serenity would die as a result, since technically they are both hosts for the SC simultaneously for a transitionary period.
In SilMil Princess Serenity took her own life while her mother was still alive. Normally that would completely disqualify her from being the next host, but due to QS's will, she was 'reborn' as Usagi Tsukino. BUT QS was also unaware that Princess Serenity willed THE SAME THING to happen of her own accord as she took her own life, only phrasing it differently to were the "person" and not just the "soul" would be reborn (long story but that's basically what happened). Which caused Serenity and Usagi to share the same 'gift' of rebirth, although Usagi took precedence given she actually had a body, while Serenity was but a "suspended existence" trapped within her.
As soon as little baby Usagi was born, the SC was fully passed down to her (and technically to the temporarily dormant Princess Serenity as well).
QS chose to die alone on the Moon waiting still and silent for her new 'daughter' to awaken so she could safely pass the Crystal her way. I see it as her final act of pure mercy and love. Not a death bed conversion per se since she wasn't looking for anybody's forgiveness or was even thinking that what she did was an overall negative, but she decided that it as her time to go and made a solely selfless act during her last few years of her life (mind you even by Sailor Cosmos' standards, QS is very old. She lived a LONG life, so her waiting on the Moon to die for even like 1000 years is pretty negligible given time moves much faster for her).
Her body is still on the Moon lol.
