Fullmetal Alchemist by Hiromu Arakawa
Edward and Alphonse are two brothers who have witnessed more than their fair share of tragedy. Abandoned by their father for unknown reasons, they are also burdened by the death of their terminally ill mother, leaving them to care for themselves. Determined to use alchemy to restore their mother's life, these two brothers find themselves on the receiving end of an experiment gone wrong. Edward finds himself without a leg to stand on (literally), and Alphonse looses his physical body altogether. In a last ditch effort to save his brother's life, Edward fuses his brothers soul to a suit of armor at the cost of his own arm. With few options remaining, Edward joins the Military and becomes an alchemist for the state. After being given prosthetic limbs, both brothers set out on a quest for the Philosopher's Stone, a mysterious but powerful object with they believe can restore their bodies to normal.
This entire series takes place in a world where alchemy is real, and quite common. The Philosopher's Stone is a much sought after item and is based on an actual legend, which you can read about here. If you like stories of human strife coupled with sci-fi elements, this might just be the series for you.