I'm Just a Side Character, but I Became the Guardian of the Marquess Family's Heir-Full Color

I should have died in the accident, but when I woke up, I found myself inside my favorite novel...To make matters worse, I'm just a side character?!
According to the story, the duke and duchess have disappeared, and all the servants are about to be fired...I've made up my mind. I'm going to live as I please! Or so I thought. Somehow, I've ended up as the guardian of two orphaned twins?! This wasn't supposed to be my role, but how could I abandon them? Just as I resolved to take the twins on their journey...