As a human, Hellmenzer did nothing but await the embrace of death. Illness confined him to his bed, leaving him to ponder the meaning of his existence as his vitality waned. Yet when Sentsels appeared and turned him into a demon, his new body was able to repel his old disease. That is when Hellmenzer finally realized his life's purpose: to serve the white demon who saved him.
Could be obtained from Boss Reward Chest during Dark Horizon
Was Hidden Boss in Infinite Realms Event.