Grimon

Grimon is the het ship between Grace Monroe and Simon Laurent from the Infinity Train fandom.

Canon
Grace saved Simon's life when he was 10 years old and they've been together ever since. They lead the Apex together and are shown to be incredibly close. Book 3 features them as the protagonists and follows their journey after getting separated from the rest of the Apex.

In the first episode of Book 3, Simon gets trapped in the Unfinished Car while the other Apex kids escape. Grace stays behind to rescue him, putting herself at risk as well. Because Simon is injured, he holds onto Grace while she carries them to safety. They end up being sent dozens of cars away from the Apex base and have to travel back together. Grace remarks that it will be "just like old times, you and me".

Simon and Grace make their way through the Jungle Car, with Grace playfully teasing Simon along the way. They meet a young girl named Hazel and decide to take her back to the Apex. In the Debutante Ball Car, the two of them dance together and Simon blushes when Grace comments on how well they work together.

A blizzard forces Grace and Simon to stay in Samantha's house, much to Simon's dismay. Simon accuses Grace of not caring about his feelings of being trapped with the source of his childhood trauma. Grace apologizes to Simon and reveals to him that her number is beginning to decrease, and that she didn't want him to see her like this. Simon reassures her that he is there for her and that they are still a team.

Their relationship takes a turn for the worse after Simon kills Tuba. Simon brags about his feat to Grace, who becomes frustrated with him and goes to comfort Hazel. Grace comes to terms with her increasing sympathy for denizens and can no longer support Simon's cruelty towards them. Realizing that Simon will kill Hazel if he discovers she's a denizen, Grace promises Hazel that she will hide it from him. Simon notices Grace's change in attitude and secretly returns to Samantha in a desperate attempt to return Grace back to her old self.

When Hazel's identity is revealed, Grace pretends to be just as surprised as Simon to avoid angering him. Simon uses the robots Samantha gave him to tape Grace's memories while she is asleep. He finds out that she had been hiding the truth from him and feels completely betrayed. After they send Hazel off with Amelia, Grace snaps at Simon for treating their friend like she was nothing. Simon responds that he was Grace's friend first. He activates the mini-projector and forces Grace to relive her memories, joining her shortly after. Simon notes that the train came to her to give her a purpose. He delights in seeing her exaggerated memory of the Conductor, but Grace feels the memory is off and the image corrects itself to Amelia's real disguise at the time. Infuriated at the corrected memory, Simon accuses Grace of lying to him just like everyone else.

Grace then sees her first memory of Simon, saving him from a Ghom after Samantha left him behind. Once safe, the young Simon cried at how he was left behind while the young Grace calms him down. When he asks her how did she get her number so high, she tells him that she is "really good at the train." From there, Grace and Simon's friendship grew as they teamed up to take on the train, forming the foundations of the Apex. Simon scoffs at the memories, again accusing Grace of lying. Grace denies she lied, but is then forced to see the moment she told Hazel that they won't tell Simon about being a denizen. Grace attempts to explain herself, but admits that she didn't tell him because he would have killed Hazel. Grace tries to apologize but Simon, whose number has now reached his neck, refuses to hear from her anymore. Accusing Grace of betraying the Apex and him, Simon leaves her trapped in her memories and walks away with no means for Grace to escape, the tape looping the moment Grace told Hazel that they won't tell Simon about Hazel's denizen status.

When Grace finally escapes and makes her way back to the Apex, Simon reveals himself as the new leader. His number now exceeds Amelia's current value, and he once again accuses Grace of betraying them all. Grace attempts to reason with the Apex about everything she had learned, but Simon continues to say she is unfit to lead and orders her to be executed.

Grace breaks away from the Apex members and confronts Simon on the bridge. She admits to Simon that she did what she had to do to keep Hazel safe and that they can still change, which lowers her number considerably. Simon refuses to acknowledge the possibility of change, which increases his number considerably. He engages Grace in a fight and the two battle. In the middle of the fight, Grace attempts to reason with Simon one last time, but finally acknowledges that she isn't responsible for his problems and that she doesn't owe him anything. Simon retorts, claiming Grace owes him everything. The two are attacked by a Ghom and Simon begins to fall off the bridge, but Grace catches him in time. When Simon asks why she saved his life, she simply says she doesn't know. Without any warning, Simon kicks Grace off the train to its wheels, horrifying the Apex members as she had just saved his life. Simon laughs and cries in satisfaction, sadness, and mad resignation that he had just killed his best and only friend. Grace is flown back to safety thanks to the origami cranes, leaving Simon dumbfounded. The Ghom reemerges and attacks Simon. Grace tries to reach him, but she is too late. She can only watch as the Ghom horrifically kills Simon and subsequently explodes moments later. Grace collapses and cries at the ashes of her former best friend.

Fanon
The tragic end of this pairing has led fans to imagine what would've happen had things progressed differently. The creator of the show has confirmed that Grace and Simon had romantic history in response to fans' interest in their relationship. They are one of the three main ships in the Infinity Train fandom alongside JessLake and Rymin.

Fandom
FAN FICTION