Tsubasa: RESERVoir CHRoNiCLE, Fullmetal Alchemist Recommendations
Fullmetal Alchemist and Tsubasa RESERVoir CHRoNiCLE deal with the lead protagonists trying to get something back that deals with one of them. To get to the thing they want, there is some conflict with an opposing side which is made up by a majority of the antagonists. FMA and TRC share the same genres as well.
Tsubasa Reservoir Chronicle and Fullmetal Alchemist are both shounen action series that are heavily plot-driven. They both start out as a light-hearted quest for a certain magical artifact(s), but after innumerable plot twists become very dark indeed.
Both series are fantasy with a great cast of characters and both of their stories get dark and twisted the more you read. They both also have shounen elements, as well.