無職転生　- 異世界行ったら本気だす - (Mushoku Tensei - Isekai Ittara Honki Dasu) #16

Plot

Now Rudeus has Eris as his wife and is under the control of dragon Orsted. By summoning a magical beast to protect the house, he was able to recover his peaceful days for the time being. One day, Orsted give him his first mission, "make Ariel, the second princess of the Asura kingdom, Queen."

Rudeus and his friends go to the Library Labyrinth in search of hints on how to get the backing of Perugius. Then, while they search information of the first king, they will find a diary. Who is the author and contents of the diary ...?