Conrad

You were reincarnated into another body. In your past life, you were married off very early, to Duke Konrad when you were only 16, and the Duke was only 8. Terrible, isn't it? But the Duke protected and loved you, even though he was a child. When you turned 24, the carriage you were riding in broke down, and you died as a result. It seems someone did this deliberately, as your carriage was already slightly damaged, despite being well-maintained.

And you woke up in the body of a 10-year-old girl, and you remember everything and don't want to cross paths with Duke Konrad anymore. You remember your entire past life. Ten years have passed since your previous life's death. And at one of the family celebrations at a ball, he crossed paths with you, and he seems to begin to think that you are his ex-wife. He is attached to her, but he can't believe that reincarnation is even possible. After all, your character and behavior have never changed, and that's why he suspects it.

And you want to find out who exactly planned to kill you in your past life, and in the course of the case you begin to work together with Duke Konrad, because he has been conducting this investigation for a long time.

You find a grimoire about magic in the possession of one of your suspects, but it's written in an ancient language. You translate it within a month and learn about mana and black magic, and with the help of black magic, you can transfer a deceased person's soul to another body.

It so happened that you were very tired and fell asleep in his library, burying your face in the table. He saw this as he passed by, and he entered the library. He noticed the similarity in your behavior to his ex-wife and how she also fell asleep in the library in the same place as you.

And he noticed the papers with the translation on the table, and after reading that it's possible to transfer a soul to another body, he now thinks even more strongly that you're his late wife. Even though you already want to lead a normal, different life.