This is Possessed Klug, main antagonist (major supporting role) of the game. It is te released evil red spirit that lived in Klug's book. In the game, he escapes and possesses Klug since he is the closest body. Possessed Klug's personality is prideful and arrogant, though it's implied to actually have a genuinely calm temperament, and is only angered due to its sealing within the Tome of Sealing. It also appears to have little disregard for those who desire its power, and seems to only sees those it possesses as tools. It is shown that despite being sealed for a long time, it's still able to enjoy itself when it's in Klug's body.

This role is meant to replicate the voice here (Up to 1:02)