I have a Martian and Project Hail Mary crossover idea.
The mark that Graces old girlfriend dated after him is mark watney. (Also let’s just say that tau ceti is less far then it is in canon so the Hail Mary makes the round trip in a little less time)
The pre-hail Mary launch story is that a twenty something year old Mark steals Grace’s girlfriend. He does this because he thinks he likes grace’s girlfriend and hates grace. What he’s actually doing is misinterpreting his stupid 20 year old brain. He realises this after actually talking to grace’s former girlfriend for once and immediately breaks up with her. He tries to apologise to grace but through the weird immorality of his girlfriend and marks dickish moves, grace doesn’t want anything to do with him. Mark ends up pining for him from a distance and trying to apologise more times.
Eventually grace disappears. Mark can’t find him anywhere. He’s in none of the usual spots Mark sees him in when stalking him. Until he sees him on the news as the scond in command of Eva stratt the leader of the petrova task force??
He watches as the Hail Mary launches. As the man he loves but who will never love him back disappears on a suicide mission. He sets on the path to be an astronaut in honour of grace.
Time skip. Grace and Rocky either decided to travel to earth together or they made it to erid and very quickly made their way back to earth. I’m saying made it to erid and they made their way back to earth and there is a eridian ship a couple of months behind them because I <3 Adrian.
Mark is stuck on mars per canon. What diverges is the Ares III somehow does not succeed in retrieving him. I’m not sure whether to do it so they never made it back to mars or not. It would be fun if they succeed at slingshotting from earth but miss the opportunity of picking up watney. So they’re heading back to earth feeling despair at the fact their friend is going to starve to death on mars. NASA is full of a bunch of people in tears. But then there’s a transmission from the Hail Mary.
Once everyone is done freaking out and confirming they’re not hallucinating they organise the retrieval of Mark by the Mary. Grace assumes that this is just another Mark Watney and not the Mark that Rocky now hates. He is wrong. They complete the manuver and get mark abord. Mark takes off his helmet and grace is like oh shit this is totally my mark and he totally stinks. Mark gets out a “Grace?” before passing out.
Mark wakes up to a face he never thought he’d see again. Is he dead? Is this his brain constructing the figure of all his regrets in life in the last moment of his neuron’s firing rapidly? Grace greets him hesitantly. Mark immediately starts crying. He falls off his bed and onto his knees (he will regret this later) and starts apologising over and over again for all the things he did. Rocky barges in and Mark passes out all over again. He wakes up to Grace fussing over him and now he’s just convinced he’s in heaven.
Eventually they catch up to the ares iii because the Hail Marys faster and I also think it would be funny for outsiders to see the insanity of A. Their science idol they all thought was dead B. A literal rock alien and C. Mark Watney being down bad for grace.
They find out how mark actually met grace because all they had heard out of mark was some poetic shit about his eyes when he was really drunk. Grace gets to marvel at the changes in technology since he left and eat something other then his own flesh and taumeba slurry. Rocky gets to see more humans and roll around more space for enrichment.
Throughout all this mark slowly manages to convince grace he’s genuine in his affection and that they should totally smooch.
Throughout this graces perception of mark goes from “oh that asshole 20 year old that all ways tries to look down his nose at me despite being 2 inches shorter then me” to “oh that asshole that convinced my girlfriend to break up with me and to start dating him only to immediately break up with her and start apologising to him for some reason??” To “sad sad pathetic wet cat who is sobbing on me damn I should date him.
Marks perception of grace goes from “Ha I should get this man l totally very much hate girlfriend to break up with him because I totally hate him and he shouldn’t be dating someone” to “Oh my god that teacher is hot, why did I make him hate me I need to apologise” to “ hngh my husband who died at war how I miss you so sob” to “PLEASR PLEASE IM SO SORRY”