Alphonse Heiderich is a young German rocket scientist living in Munich in 1921, where he becomes a close friend and roommate to Edward Elric after Edward is sent to this world from his own. By his name and appearance, which bears a striking resemblance to Edward's younger brother, Heiderich serves as the parallel counterpart to Alphonse Elric in this alternate reality. Heiderich is easygoing, kind-hearted, and generous, exemplified by his willingness to shelter a Roma girl named Noah from the Thule Society despite the growing prejudice against her people. He is a man of science with an inventive, practical mind, having studied rocketry under the renowned Dr. Hermann Oberth in Romania before returning to Munich to pursue his research. While he enjoys hearing Edward's fantastical stories about alchemy and another world, he doubts their truthfulness and is hurt by Edward's eagerness to leave, as well as his assumption that the people of this world are merely part of a waking dream. Despite disagreeing with the racist concepts of the Thule Society, Heiderich accepts their sponsorship to fund his projects, driven by a desperate need to prove his country's scientific worth and leave a lasting legacy. This urgency stems from a fatal lung disease, which is implied to be lung cancer caused by the inhalation of rocket fumes, causing him to suffer from violent coughing fits and eventually cough up blood. Heiderich hides the severity of his illness from those around him, putting on a brave face and dismissing his symptoms as minor to avoid causing concern. He is responsible and self-sufficient, often taking care of household matters while Edward remains preoccupied with thoughts of returning home. Heiderich is completely unaware that the Thule Society intends to use his rockets not for peaceful exploration but to invade and plunder Edward's world. When Edward confronts him with this truth, Heiderich refuses to stop his work, leading to an intense argument during which his illness is finally revealed. In a poignant final act, after reminding Edward that he and this world are real, he helps his reluctant friend return home by sending him back through the opened Gate in a two-seater rocket. Shortly after launching the rocket, Heiderich is shot and fatally wounded by Rudolf Hess, dying with a smile on his face as he watches Edward make it safely through the Gate. Throughout the story, Heiderich is defined by his hidden pain, his quiet determination to matter, and his ultimate sacrifice, making him a tragic figure whose death deeply affects Edward.