Undyrus

Undyrus is the friendship between Undyne and Papyrus from the Undertale fandom.

Canon
Papyrus met and befriended Undyne sometime before the events of the game. It is implied that Papyrus wanted to join the Royal Guard because of Undyne, as she was already part of it and he hoped he would find more friends that way and finally earn people's respect. Papyrus was so determined to join that he waited outside Undyne's house for hours to convince her, fully believing that he got what it takes. She eventually realizes that he's too nice to actually harm anyone, but offered to give him cooking lessons instead to let him down gently. Despite liking him as a friend, Undyne refuses to let him join until he shows his worth by capturing a human.

Neutral Route
Should the player befriend Papyrus instead of killing him, he will try to convince Undyne to spare the human. Undyne does not respond and continues her pursuit of the human child with intentions to rip their soul out to give it to King Asgore. Papyrus is at first distraught, but then admits that he can't actually refuse his best friend and stays loyal to both Undyne and the human, trying to avoid confronting either directly. He tries to come up with a scheme to avoid either of them getting hurt, but it backfires, leading to the human having to take care of Undyne on their own.

While Undyne is chasing the human, Papyrus will call them, telling them that they and Undyne should just hang out instead. Should the player run to Undyne's house while being chased, Papyrus will already be there waiting for them, but Undyne is not in the mood for casual hangouts.

Only after letting Undyne chase them to Hotland and letting her overheat in her armor is a hangout as Papyrus requested actually possible. However, the human has to either give Undyne water or pour it right on her to actually successfully resurrect her and have her unlock the door to her house. Should they refuse to give her water, she will disappear, with backtracking to her house still having Papyrus standing there, telling the human that Undyne suffered a heatstroke and has to recover. It is implied that he was the one who found her in Hotland and carried her back home. If the player chooses to outright kill Undyne, Papyrus will still be standing in front of her house, none-the-wiser.

If the player had killed before meeting Undyne and saving her, she will tell Papyrus that she doesn't want to hang out with a murderer, which confuses Papyrus as he didn't murder anyone and is too innocent to suspect the human of doing so.

Should the hangout actually take place, Papyrus will appeal to Undyne's competetive nature, by presenting the act of befriending her enemy as a "challenge". He then promptly excuses himself and jumps through her window, leaving glass shards all over the floor.

True Pacifist Route
Befriending both Papyrus and Undyne is one of the requirements of getting the best ending.

Another (besides having zero EXP) is trying to play wingman for Undyne and Alphys, in which case Papyrus will help Undyne out by coaching Alphys to raise her self-esteem high enough for Undyne to have no qualms about dating her.

In the final battle, Papyrus will call Undyne and every other character under Flowey's orders, believing that its in order to help the human child befriend Asgore. However, it was actually a ruse by Flowey in order to get every monster in the Underground to meet at one place to absorb their souls all at once. Before Flowey could kill the human, Papyrus and Undyne will work together to deflect his attacks, showing how much they care.

After Flowey is defeated, Undyne and Asgore will disband the Royal Guard under Toriel's orders, causing distress for Papyrus as everything he did in the story was for nothing.

Fanon
Some support Undyrus romantically, but due to respect for Alphyne and general agreement that Undyne is lesbian, most ship it platonically.

Fandom

 * FAN FICTION