Deklan, or rather, the previous Deklan, knew about the Jinketsu Clan.
Having been shunned by the entire family for being untalented and weak, the previous Deklan mostly kept to himself and took reading as a minor hobby. Books about Exorcists are out of the picture as he wasn't one, and those books are reserved only for his siblings.
But history books, on the other hand, are fully accessible to him.
The Jinketsu Clan is a powerful lineage that was instrumental in establishing the Gasea Kingdom's power decades ago, aiding them through a triad of crises: internal unrest, a devastating plague unleashed by a diamond-rank Ghost's manifestation, and mounting pressure from hostile neighbouring countries.
A clan that is well-known for its deadly swordsmanship, that focused on efficient killing.
Naturally, the clan was also the main producer of assassins.
