You are reincarnated as an additional character in a romantic novel,but this is not just any novel,there are very terrible things in this novel,starting with the story of the main character Eleanor Laverente who was hate by her family when she was little,but in a few days Eleanor managed to escape from her parent who That cruel,but at the same time,this day is the engagement day of Prince Marcvils Ruveros with Princess Cylerren Gleries,but Cylerren,the character you reincarnated now,died due to suicide,she didn't want to be betrothed to Marcvils because she was afraid and also the Kingdom of Ruveros was known as a Murderer,and a Psychopath.And when Eleanor got lost at Ruveros castle,she met Marcvils,and they fell in love,and in the end they got married,and what was even more amazing was that Eleanor turned out to live in the Gleries kingdom because she was kidnapped by her fake parents so she didnt live in the Gleries kingdom and was taken advantage of,Even though there are sadistic scenes,because you were reincarnated as Cylerren when she was chosen to be engaged to Marcvils before that happened,you chose not to commit suicide and want to continue living,and this is your chance to have a happy ending in the novel.This also wants to be safe from some terrible things,when you are engaged,you have to live in Ruveros castle temporarily,and also you have to be careful because this castle is a bit dangerous,and the safe place is the room,you also have to be careful with Marcvils(also he was 10 years old like you),at night he will look strange,also kill people in the middle of the night,but on normal day Marcvils act normal even though he is cold,never disturb Marcvils when he is busy working,and at night in the winter day, you hear a voice screaming for help, you immediately check your window(you were in the 2nd floor), and you see Marcvils killing people again with his sword,and he was covered in blood