This is an AU Crossover idea which ends up making Kasumi have to take on the role of Moon Princess and possibly also Sailor Moon.
This all started this morning with a question of What If. What if Usagi died in her first fight as Sailor Moon. That got followed by why would she have died? Well What if Tuxedo Kammen wasn't there to rescue her? Why wouldn't he be there. What if he was sitting in the front seat with his parents when the car crashed and died with his parents in that car crash?
Don't worry there are heirs to both the Terran and Lunar lines other than Mamoru and Usagi in this idea. I think I'll start with the inheritor of Tera's mantle first.
I was thinking, at the time of Mamoru's Death, Nodoka Saotome could be gardening in her yard and witness a long stem rose almost instantly grow out of the ground in her garden. When she picks it up it transforms into a Henshin stick. Starting her life as a Vigilante crime fighter almost 8 years before the first exploits of Sailor V.
The only criminal she's unable to confront is her own husband Genma. When she almost catches him her years of celibacy, due to being faithful and waiting for him to return, leaves her in daydream mode. Fantasizing for the day he does come back to her.
Nodoka is the closest descent relation to the long lost line of Endymion. The line able to trace its way through first and second born all the way back to the Princess of earth and little sister to Mamoru's past incarnation. She survived the fall and changed her name to hide from the ambitious seeking to pick up the pieces from the fallen Earth Kingdom. If it wasn't for Queen Serenity sending her brother and his mantle of the Guardian of Terra to the future to be reborn there might have still been 1 Senshi other than Pluto left in the solar system after the fall.
Now that I made you read that wall of text, a little more teasing.
Along with the mantle comes an awakening of instincts and memories connected to it. Its lost to the Reborn Senshi because the forced Reincarnation effectively had them born with their mantles already bestowed to them. So by the time they were old enough to understand them the memories gained through the mantle had been mostly forgotten. Nodoka finds herself lucky that Ranma was born before she took on the Mantle of Sailor Terra otherwise it is almost certain that Ranma would have been born female, as the magic can effect that and seeks to ensure it has a proper heir.
The reason Endymion wasn't Female is because he was born as his father was when the previous Sailor Terra was still active. She ended up passing away before his little sister was born so his father was the Heir apparent but passed it on to him.
What does this mean for Ranma. In this idea when Ranma gets cursed at Jusenkyo hot water doesn't work to reverse the curse. But after meeting the Amazons Ranma discovers she can create roses and using one as a focus she can will herself back to her male form. Genma of course insists on Ranma using it to return to male at every possibility but Ranma instinctively feels like he's abandoning his honor and duty when in male form from that point on.
Of course there are differences from Cannon. Like Genma's reaction when Ranma doesn't turn back just gets a quadrant marked circle appearing on her head when the water is poured. That mark appears again when Shampoo cups her chin to give the kiss of death. It instantly stops her from doing so as she is shocked from seeing she was just beaten by a Legendary Warrior Princess of Tera. The Elders end up telling Ranma about what the glowing mark means and the ability to manifest Roses.
Edit: Oops left out one little detail. Cold water will still put Ranma into Curse form. But the only way out is manifesting the rose and willing the change.
Ok this has been Saotome this Saotome that its time for the reason the topic is titled Tendo Moon. It stinks when things fade that you were thinking about while waking up. So the next bit might not be fully coherent.
In the Silver Millennium Queen Serenity had a younger sister. Like the Princess of the Earth Kingdom surviving the fall she changed her name but unlike her fellow surviving noble she established the Tendo family. Decades even centuries before the rise of the first Samurai. But the nature of the Serenity line keeps the Matriarchs of the family from ever lording it over other families that see themselves as noble. The first born always having lighter shade hair than her sisters seems to have an innate inner peace. Their hair lightening another shade when the past generation's first born passes away. This pattern continues all the way to the Tendo's of this story. Kasumi is direct, no second born about it, descent from Serenity's Sister. And when Usagi passes her hair goes silver as the mantle finally has the freedom to pass to the surviving line. The same kind of memories are bestowed on her but also the feeling of responsibility to the station that is Princess of the Moon Kingdom. Also in Usagi's passing all the other Senshi get awakened to their powers. Sadly they had their mantles already but now their Henshin rods have appeared to all of them and only Hotaru in possession of Mistress 9 is unable to take it up.
Kasumi is a student of Anything Goes. She was trained in all the basics just as her sisters were before their mother died. How will these changes effect the story of Sailor Moon? And will Nodoka pass on the Mantle of Sailor Tera to Ranma? Its set up at the start of both series Anyone want to take up the challenge to see where these changes go?
Edit again: One other detail I left out. The reasoning I had for Luna still finding and awakening Sailor Moon first is because she joined the Lunar court after the passing of Sailor Tera and as far as her damaged memories can tell her there wasn't a Sailor Tera at all in the Silver Millennium.

