Shishosei

Overview

Concurrent with the sudden and mysterious death of the youth who was to be selected as the next king, the "Library Tower," which housed all the books of the country, was sealed off. However, deep in the recesses of the tower, where no one should have been able to enter, sat the one who was known as the "Shisosei." In the palace where rumors flutter about, conspiracies begin to swirl. What is the astonishing reality behind the connection of the youth's death, the Library Tower, and the country's secret tool, the Shisosei?

Source: AniList