Fullmetal Alchemist

In this world, alchemy is based on understanding the inherent laws of matter: understanding, decomposing, and reconstructing. Alchemy must be conducted according to the law of "equivalent exchange": in order to obtain something, it needs to be exchanged at an equal cost, and if the cost is not enough, any part of oneself (such as a part of the body, memory, etc.) needs to be taken away as compensation.

Edward Elric and his brother Alphonse Elric deeply miss their mother who passed away when they were young. In order to see their mother again, they practice the biggest taboo in alchemy - human body alchemy. However, due to the backlash during the refining process, Alphonse lost her entire body and Edward lost his left foot. In exchange for his younger brother, Edward sacrificed his right hand to refine his brother's soul and fix Alphonse Elric's soul on a suit of armor. From then on, Edward and Alphonse embarked on a journey to regain their bodies in order to retrieve everything they had lost.

Edward's lost right arm and left leg were replaced by steel prosthetics called "mechanical armor", hence he was awarded the title of "Steel" and known as the "Fullmetal Alchemist".