Just wanting to get to know the other members of the club! I'll go first:
I was probably around 9-10 years old when my sister was telling me about this new game all her friends at school were playing on their school laptops. At that point in time in our middle school it was common for kids to pirate games (NOT CONDONING btw, pls support game devs, especially indie devs), download them to flash drives, and pass them around to each other so they could all play. My favorite thing in the world was to watch her play these games, so when she brought home Undertale and told me how cool it was, I was really excited. Every night after our parents went to bed (we'd get in trouble if they found out she was not only pirating but playing on her school laptop), we would sit at her desk and I'd watch her play. It's a really nostalgic memory for me and I think it's why I latched on so hard to the game.
As for Deltarune, I actually thought it was a fangame at first, so I didn't really seek it out since I didn't really play a lot of fangames. I eventually did realize it was official though and played both chapters.