I Receive Directions To Become The Supreme Demon In My Sister's Novel

When Lin Yu woke up, he was shocked to learn that he was transmigrated to the fantasy novel his younger sister had written. To make matters worse, his character was a stepping stone for the main protagonist.
Not only did his childhood friend would marry the main protagonist, but he would eventually become a demon in the end and get decapitated by the main protagonist.
Fortunately, the notebook that he had received from his sister on his birthday had arrived at the new fantasy world with him. It allowed him to communicate with his sister.
“That’s right! Go to the hill behind the village and look for a tree that has been struck by lightning. Walk around the tree clockwise three times, and you’ll enter and secret dungeon! You can learn a God-tier Martial Art there!”
“What? Pills? Look for a Mr. Xu at the East Market! Buy the ring he’s selling. There are a lot of different pills in it, enough for you to eat as many as you want!”
“Oh! Don’t forget to locate the Moonlight Treasure! It’s a Divine Item that allows you to move through dimensions. I want to go to that world for a holiday too!”
After being given all the information, Lin Yu only had one question in his mind. “Sis, where is your future sister-in-law?”