Typically, Stein is a hedonistic scientist whose greatest pleasure is dissection and observation, which persisted from childhood to adulthood.Due to this, Stein claims sees everything in the world (himself included), as an experiment. He developed sadistic tendencies (due to his sensitivity to madness), has a high intelligence, and a driven personality. His smiles typically are also full of sadism and serve to highlight the latent madness inside of him. During his childhood and adolescence, he had a tendency to want to dissect everything. He was stopped by his first weapon partner, Spirit Albarn. He was shown to have little empathy even towards his friend/partner, and it is thought that he can’t experience love. Though he has shown that he can love through tense moments. He is a meister that can change his soul wavelength, meaning he can match with most if not all weapons. He also has a twisted and sadistic sense of humor, often riling up others (both students and peers alike) for his own amusement. Being self-aware of his behavior coming off as suspicious and creepy, he enjoys playing it up to them. Stein appears as a muscular, lean male with silver-gray hair, large round glasses, and a handsome face. His most notable trait is the large screw through his head, in which he can turn. He also has stitches all over his body, indicating experimentation. His attire includes white lab-coat with a turtleneck shirt having two different shades of gray patterns. Both clothes are covered in stitching also.