I feel like the posts where people go "just watched phm and i don't get why people ship grace with markiplier's character from another movie" are going about it all backwards. As you simply don't get the context for the ship just from watching that.
The Iron Lung movie came out before the Project Hail Mary movie. Two months before, in fact.
The ship started not because people watched PHM and decided to ship Grace with this other character called Simon. But because the Iron Lung movie fans watched it and decided to ship Simon with Grace.
Spoiler alert for both movies here, but Iron Lung is a horror movie where the main character goes through it all alone and then dies at the end. PHM meanwhile ends in a more hopeful tone where the main character gets not only companionship, but a chance at a happy ending.
People who had watched the Iron Lung movie watched PHM and noticed the similarities of the unwilling suicide missions the main characters were put through.
And then went on to consider what if Simon didn't die, but rather got transported to a different world. To someone who understands what he went through. And he gets to have a happy ending.
It started from people rescuing Simon, not from needing to ship Grace.
