OKAY YOU ASKED FOR THOUGHTS YOU ARE GETTING THOUGHTS. (No spoilers please, I’m just going to talk for a little bit!)
First of all, I love that this show makes it VERY CLEAR that Usagi and Serenity are completely different people. As far as I remember, the anime never really addressed this, and the two were functionally interchangeable. Here, they are distinct in looks and in personality. You can even see the moment when the switch happens:

Usagi, her feathers ruffled, and then

BAM BLAM KABOOM SERENITY IS HERE AND SHE TAKES NO PRISONERS
Serenity takes over as soon as her possession of “Endymion” is threatened. She seems to have a single-minded focus of MIRACLE ROMANCE, while Usagi’s interests are slightly more varied (friends, food, cats, family, et cetera). And yet, her obsession doesn’t seem like love; it seems like control. She’s the dormant goddess of horrible all-consuming jealousy that was living in Usagi’s subconscious for millennia.
Sailor Moon also becomes WAY more powerful when under Serenity’s influence, just throwing around balls of flame and creating bolts of energy like it’s just another Tuesday morning. But this massive amount of power comes at the expense of a loss of control. Serenity only wants this one thing, and is willing to risk a lot to get it. Usagi wants many things (the aforementioned friends, food, cats and family). Things that Serenity would perhaps sacrifice if she needed to.
Where I am a little lost is where the MIRACLE ROMANCE is involved. Serenity and Endymion fell in love, and their reincarnated souls found each other again in the bodies of Usagi and Mamoru. So why is Serenity’s portrayal so different from Usagi’s? Maybe Serenity and Usagi DO share a personality, but they choose to focus on different goals. Usagi has a part of her that is dangerously uncompromising, but she pushes it to the side because she wants everyone to be happy. Serenity loves her friends and family, but the bitterness of two young lives cut short turned her mind from love to revenge.
I’m just throwing around words. I don’t really know what’s going on, but hopefully the story will take me where I want to go.


