Undertale was just a normal videogame for most people. But for the player who goes by the handle of 'Frisk', it meant much more. After countless hours spent in the game, they had become quite familiar with all the characters.

One day, something unusual happened. Frisk was wandering in the peaceful town of Snowdin. He was looking for Sans, the lovable, skeleton who was somewhat of a mentor to him.

However, Frisk couldn't find Sans anywhere. He wasn't in his usual spot - the sentry post or hanging out with his brother Papyrus. Even the local grill was Sans-less.

Frisk was growing more and more worried. He knew Sans was a massive prankster and loved pulling his leg, but disappearing entirely was uncharacteristic.

As a last resort, he visited Sans's underground lab. As he pushed open the door, he almost couldn't believe his eyes. There was Sans, nonchalantly chatting with... himself?

There were several other Sanses with him. Each one looked slightly different. There was one with a hood up, another dressed as a pirate, one looked like a version of Sans from a different era.

"Sans! There you are. Who are all these people?" Frisk asked, brow furrowed in confusion. Sans grinned and shrugged, a typical casual stance.

"These? They're just my AUs, kid." Sans replied nonchalantly. "AUs?" Frisk's confusion only grew at the unfamiliar term. "Alternate Universes, buddy." Sans offered in an attempt to clarify.

Frisk blinked, slowly processing the new information. "Wait, so you’re saying these are different versions of you? From different universes?" Frisk asked, trying to wrap his head around the concept.

Sans nodded, chuckling at Frisk’s astonishment. “In a nutshell, yes.” He then introduced each of his AU counterparts, each with their own unique quirks, styles, and personalities.

They spent the next few hours chatting, laughing, and playing games. Frisk found himself surprised at how much he enjoyed the company of the different versions of Sans.

It was fascinating. They were all Sans, but they were also different. Each had their unique angle, their own version of the same characteristic humor, and their own stories.

The pirate Sans, for instance, spoke in a thick sea captain's accent and kept saying "yarrr" or "shiver me timbers". The hooded Sans was more reserved and cool, with a mysterious aura.

Time seemed to fly while they were all together. The spirit of camaraderie filled the room and even though Frisk was initially overwhelmed, he soon felt like he was a part of this multiverse family.

As the day was coming to an end, each of the AUs gradually began to fade. One by one, they said their goodbyes, promising to return someday.

Sans turned to Frisk with a soft grin, “I hope you learned something today, kiddo. These guys can be a handful but they’re good company. Just like how our own universe is unique, so is each of them.”

Frisk nodded, understanding slowly dawning upon him. He realized that every choice he made, every path he’d taken in the game, all of it could lead to a different version of Sans.

He had always seen Sans as a comforting constant in his gaming experience. Now, he understood that even constants could vary, be it in character or in universe. It was a profound realization.

They sat in silence for a while, reflecting on the day's events. Despite the absurdity of it all, it somehow felt right. It was a strange but comforting thought that even in different realities, Sans was always Sans.

The day ended as any other, with Frisk retreating to his virtual home within the game. He laid on his bed, looking up at the pixelated ceiling, his mind still buzzing from the day's encounters.

As he drifted off to sleep, he promised himself that he would explore these alternate universes more. After all, who knows what other surprises Undertale had in store for him?

This adventure had given Frisk a new perspective on his favorite game. But more importantly, it gave him a newfound appreciation for the lovable, joke-cracking skeleton.

No matter which version of Sans he met, which universe he was from, he was always pleasantly familiar. It was as if Sans had become a universal constant in Frisk’s gaming life.

With renewed enthusiasm, Frisk looked forward to his next Undertale play session. There were still so many paths to explore, so many universes to discover. And of course, so many Sanses to meet.

Knowing that, every time he logged into Undertale, he would be met with a different version of his beloved friend, Sans. With this thought, Frisk couldn't help but smile. And thus, another day in Undertale ended.