SansGen

SansGen is the slash ship between Sans and Arataka Reigen from the Undertale and Mob Psycho 100 fandoms.

Canon
Sans and Arataka Reigen are from different series, they have never interacted. Sans is from a game, while Reigen is originally from a manga series. They are both major characters in the their respective series, Sans being a supporting character or final boss in Undertale while Reigen is the mentor and boss of the main character of Mob Psycho 100.

After Sans was crowned the Ultimate Tumblr Sexyman, Toby Fox, the creator of Undertale, replied with a short story. Reigen was surprised to see he was going against Sans in the finals; Sans had been entered into the competition by Papyrus and got to the finals by doing nothing. Reigen pointed out how unattractive Sans was and became attractive himself, which boosts Sans' votes since Tumblr sexymen are unattractive. Reigen was about to drop out of the competition before being cheered up by Mob. Reigen also received a boost in votes after he showed up looking unattractive on the final day of the campaign. Reigen lost by one point even though Sans voted for Reigen; Mob voted for Sans since Tumblr sexymen are unattractive and he wanted Reigen to have self-confidence.

Fanon
Both are extremely popular characters within their fandoms, if not the most popular. They both have lots of fanart, and people will "thirst" over both characters. Because of their fame as characters and their simps, they have both gained status as "Tumblr Sexymen".

The ship started when hosted a poll where people could vote on who the Ultimate Tumblr Sexyman is. Reigen had won multiple other polls he did not qualify or qualified for with weird reasons. Sans and Reigen were the finalists on the poll. Because the poll became extremely popular on Twitter, many people made fanart of the poll, mostly tagging it under both #SANSSWEEP and #REIGENSWEEP. This progressed from them fighting to ship art.

On September 8th, 2022, Queen Elizabeth II passed away. Because of the large impact the meme was having on Twitter, fans jokingly said that the poll is what killed the Queen. Queen Elizabeth makes an appearance in some Sansgen art because of this. Many people will portray the paring alongside Sansmaeda, another infamous Sans crackship. Nagito and Reigen are sometimes shown competing for Sans' affections while other times, all three of them are in a polyamorous relationship. Some art also features Reigen and Sans together with Hatsune Miku after both of them lost to her in another poll.

Fandom
FAN FICTION

TUMBLR

TWITTER

Trivia

 * In the tumblr sexyman poll by sexymanOTD, Sans and Reigen were tied almost the entire round. However, Sans ended up winning the poll by 0.1%. The poll had 244,809 voters, and ended on September 7th, 2022.
 * In the small snippet that Toby Fox wrote after Sans won the poll, it is 'canon' that Sans won by one vote, that one vote being from Mob. It is also stated that Sans voted for Reigen.