AverageWeirdo's manga / #supernatural(261)

"In the heart of the quaint city of Westull, a colossal tower serves as the residence for the King of all Devils, Terius, and his loyal servant, Jacque. Jacque's routine of caring for his reclusive master takes an unexpected turn when a mysterious tentacle monster infiltrates the tower, launching an assault. Struggling against the creature's power, Jacque seeks help from Terius, only to be shocked by a surprising demand - the devil king insists on subjecting Jacque to the same fate, citing the necessity of releasing tentacle poison. As uncertainty about Terius's true intentions grows, Jacque grapples with the challenge of preserving his once-peaceful life as a servant in the devil's tower."