Possibilities

Davis naturally didn't have any heart or organs to speak of, as everything in his Solitary Soul Avatar was conjured using soul essence and soul force. Even though they were all something made from soul force, he could still feel fleshy sensations that a normal body could feel, and the feeling of the heartbeat was one of them, making it feel awfully similar to a real body.

Davis felt extremely uncomfortable over this unnatural beating of his heart that his expression almost snapped under the mask.

"Tell me... What have you done to me?"

"I..." Tina Roxley looked shaken with tears staining her face. She subconsciously shook her head lightly, not knowing what this masked man, no, Alchemist Scythe, was talking about.

"Oh, you're now playing ignorant?" 

"No... I-"