There was a rough mental chart Kain kept in his head whenever he thought about the upcoming auction based on what he saw while fulfilling his Black Mision last year, and the going rate for weapons.
After fighting against Kyria, Kain realized that he'd completely let his equipment slack. Due to the strength of his contracts, Kain no longer felt the need to join the battle and fight himself like he did when it was just Bea and himself with a spear.
Therefore, Kain was hoping that he had enough funds available to completely outfit himself in the best 5-star gear—5-star gear with 6 sigils (the max they can have and is typically only achieved by a Grandmaster Blacksmith).
