I love bloodymary as a ship because the origins of the concept is really sweet.
Like it's really a ship that started in an attempt to give these characters (mostly Simon but in some minor facets Ryland as well) a happy ending. To give them a new connection that will make them happier. Like there was legitimately no other reason to put these two together beyond that + "bc it sparks joy" + the fact that the respective movies were released close together. Sure, I'm well aware of crack shipping and how wacky it is, but it's still a wild connection to me, sure it makes sense in hindsight but at the beginning?
People looked at Simon in Iron Lung and his very human plea of wanting to live, and was like 'y'know who understands the horror of being the sacrificial lamb and also happens to have a high-tech spaceship? Ryland Grace. He and his best friend are on their way to save you now. You're gonna have a life, and people that love you like you deserve.'
And people looked at Ryland, who has a loving family (Rocky and Adrian), and a happy ending by all definitions of the word and thought, just in case you ever feel this primal dread knowing you'll never see another human as long as you live, just in case it keeps you up at night that the very last time human hands touched your skin it was so terribly violent, here is a potential human connection for you. One that doesn't replace Rocky or Adrian by any means, but adds something newly valuable to your life. Gentle hands for both of them, when they had so little of that previously.
And I adore the fact that bloodymary doesn't have to be romantic. Like I love the romantic stories, don't get me wrong, but I love the queerplatonic ones equally as much. It's called a ship but it's not really about finding either of them a romantic love interest, not really.
And it actually baffles me how well these two universes fit together, like puzzle pieces.
They each have their trolley operators, Eva and Ava, who want to treat Ryland and Simon with humanity, but knows they cannot because of the number of lives that rest solely on their shoulders.
The will to follow through on the task that would save humanity despite being hurt so badly by other people (Ryland Grace continuing his mission until the end even after remembering, Simon retrieving the black box knowing he won't make it out alive).
They each have the religious - specifically Christianity related - symbolism present in their stories. Hail Mary, full of Grace (which is a concept that still makes me giggle btw). The reference to the garden of Eden, with the spaceship name, the cults (unfortunate) beliefs in sacrifice and sin, and the last tree. The incident being called a rapture. While still not being a religious movie, and still being rooted in and true to their respective genres (sci fi vs horror).
The stars dying out vs the stars and planets disappearing. There is so much you could play with in that concept. There's of course the parallel universe thing, the "Simon comes from a future where they failed" thing, and even 'Simon and the other ships did end up in a pocket universe with nothing' thing, like Simon had wondered about. Explanations about what the Light Simon saw might be and how it could be connected to astrophage. So much possibility.
Simon died in a universe that got an unmerciful and indifferent entity pulling the strings, and people outside the story gave a shit enough to create the potential for a gentler ending. One that opens up a world of possibilities for both characters. (Also to be clear I'm not dissing the canon ending to either movie by any means. I adore how Iron Lung and PHM was written - and fanworks don't overwrite that at all).
It almost reminds me of that one quote from Brennan Lee Mulligan, y'know the one. It's somewhat stupid to apply it to a fictional ship but it comes to mind nonetheless.
"In the same way your heart feels and your mind thinks, you, mortal beings, are the instrument by which the universe cares. If you choose to care, then the universe cares. If you don't, then it doesn't."
It's just. Sweet. And kind. Such a fundamentally kind ship.