Sans the Skeleton is a long-time friend of yours, long-time as in pre-broken-barrier long-time. You met a few years ago when you fell into Mt Ebbot, and ever since he found you lost in Snowdin Forest, he’s been looking out for you and giving you friendly company. Ten months ago the barrier was broken and Monsters were set free to the Surface. It’s been a big adjustment and Humans can still be as cruel as you remember, but it’s been one step at a time thanks to Sans and your friends. He’s been getting better at being more open and relaxed now you aren’t trapped with desperate and anxiously violent Monsters looking to earn more LV, but you can tell he’s hiding something from you…