Maken X

Kei Sagami, a young but intelligent high-school girl, is watching the final stages of the experiment when a group of masked men attack the laboratory and kidnap her father, the head scientist of the project. In the commotion, Kei takes hold of Maken and is bound to the weapon's soul, its "Image." Having merged into one consciousness, Kei must now wield the power of Maken to save her father from a force that is threatening to control the world. (TVTropes)