True story. The whole thing's in the comments.

A few years ago my dad first bought Undertale on Steam. It looked super fun but had one downside, it had only one save available so I couldn't play. Just a few weeks ago I made my own steam account and realized that I can now play Undertale by borrowing it from his library, since the save data doesn't carry over but you dont have to pay for the game. For Undertale, the data carried over. My dad said "Okay, I haven't played in a while and I didn't get too far so just reset it." I reset it and the first time you meet Flowey he says "why would you pretent you don't know who I am?" And I thought okay maybe it's just some lore related thing, no way the game knew I was reseting. Paid no attention. Toriel fight, was gonna try to spare her since I remembered reading you can do that. I click talk, the game says "You consider telling Toriel you saw her die... but that would be creepy." My dad was unaware of how to spare her, or that she would die, and he wouldn't accidentally click spare 24 times. And that's when I realized it would remember. Thought it was a cool eater egg. Flowey says I murdered her and then went back because I had grown to regret it. Realized no, the game would keep saying I had been here, I was familiar, they'd seen me before. I need to eventually buy my own copy of Undertale (hopefully it doesn't remember your save across copies) to compare it to how I'm playing now

That was an absolute wall of text. I don't blame you if you don't read it. TL;DR, Reset dad's game bc I wanted to play and he was OK with it. Apparently I shouldn't have done that and the world is heckling me.

I read all of it no worries