Yo-kai Sangokushi

While exploring the library of the Springdale Elementary School, Jibanyan, Komasan, and Usapyon find a book titled Yo-kai Sangokushi, which they are teleported into.
During the beginning of the game, the player chooses either Jibanyan, Komasan, or Usapyon, and the plot of the game centers around the Yo-kai the player picked.
Inside the book, the three Yo-kai are separated and turned into military leaders.
They later find out that they need to find eight jewels to return to the real world, which becomes the focus of the game.

Résumé

Yo-kai Sangokushi is a turn-based tactical role-playing game developed by Koei Tecmo and published by Level-5.
It's a crossover between the Yo-kai Watch and Romance of the Three Kingdoms series.