The Karsus Crown and accompanying Nether Stone, along with the Karsus Annals and Sachiat's Code... Leon handed over most of his spoils from Ferren to Tassera, leaving Sain's Necromancy Spellbook to reward Laksha whenever she achieved merit.
Indeed, Leon could be completely open with Tassera, whom he had known since his early teenage years and who had now become his Queen. He trusted that she would stand by him in times of danger, but he regarded Laksha merely as a competent subordinate.
Tassera spent half a month in the Mage Tower, completely immersed in research, receiving meals and drinks from servants.
As for Leon, upon returning to Watchtower Port, he finally had access to a suitable Melting Furnace. He dismantled the Hard Head Hammer from Rosymorn Monastery to extract the crucial Divine Blood, carefully integrating it into his Fine Gold Greatsword.