Frans

Frans is the non-binary between Frisk and Sans from the Undertale fandom.

Canon
Frisk and Sans first meet in Snowdin Forest located in the Underground, where he introduces himself with a whoopee cushion and explains about himself and his brother. It results in a funny scene with his said brother, in which the Snowdin arc of the game begins. Throughout the arc, Sans shows up in random places and along with his brother.

His next notable appearance with Frisk is when he invites them to Grillby's for a chat. Sans asks about a talking flower (in which the player can make Frisk say yes or no) that hints towards Flowey, though Sans covers it up with the idea of an echo flower. During this scene, Sans "accidentally" ruins Frisk's fries or burger by dumping the entire ketchup bottle on it. Sans says Frisk can have his instead because he wasn't going to eat it anyway.

Later in the game during the Hotland arc, Sans is seen running a hotdog stand which will lead to a funny scene with Frisk. If the player's inventory is full, Sans will start to stack hotdogs on top of Frisk's head until he is unable to reach anymore.

Near the end of the Hotland arc at the MTT Hotel, Sans invites Frisk to dinner within the hotel. What occurs is that Sans tells a story about a lady beyond a door in Snowdin he used to tell knock-knock jokes with. The lady had apparently told him to keep watch and protect a human if they ever go through the same door, which he complied. He said to Frisk that if this hadn't happened, "You would be dead where you stand." He brushes it off as a joke afterward, but it's unknown if he was joking or not.

The last Frisk sees of Sans in the Neutral run is in the Judgement Corridor where Sans will judge Frisk and the player for every EXP and LV they have earned throughout the game, as it was revealed that these stats mean different things. Reactions vary depending on the stats, but the most friendly is that he claims Frisk has not obtained LV or LOVE, but love inside of themself and leaves them to what the Underground's fate is.

If the player manages to get a Pacifist run, Sans appears near the end of the game along with all the other friends Frisk got during their adventure. Once Flowey- or Asriel- appears, Frisk saves Sans along with the others by reminding him of the interactions and the friendships they both had along with Papyrus.

At the end of the game where everyone looks off into a mountain, Sans does not interact much with Frisk but is still friends with them.

Fanon
This ship has received a lot of backlash due to Sans seeming much older than Frisk is, with Frisk having no known age other than what seems to be a child. To make up for this, people often ship an adult version of Frisk with Sans instead. Frisk is often portrayed as female in Frans, but there is no canon gender for Frisk. Because there is no seen dialogue from Frisk that isn't chosen by the player, there aren't many gateways to being able to find romance between their relationship.

Popular rival ships for the pairing include Soriel, Fontcest and Frisriel. There are also people who choose not to ship Frisk or Sans with anyone.

Fandom
AO3

DeviantArt
 * frans tag on DeviantArt
 * friskxsans tag on DeviantArt
 * sansxfrisk tag on DeviantArt