That Mysterious Child Undertale AU's x Smart! Child! Music Maker! Hacker! Reader

You were very smart for a 9 yr old. You loved books, and you didn't watch TV much, unless it was educational. Your parents didn't care for you, like they cared for your older brother. They treated him like a perfect child and treated you like you weren't even their. You were always home alone and you liked it. You made music and you wrote books online, so your dad was proud that you 'becoming one them of them'. But secretly, you were writing and making music. When you fell into the underground and met the monsters, things get crazy lit. You're also a hacker, so you hack into things, but not monsters or the world, or else...something bad would happen.

You know the underground and the monsters, like the back of your hand. You know the codes and timelines