The Mangekyō Sharingan gives the user enhanced power of the Sharingan's generic abilities and each eye can also awaken different powerful techniques. Some wielders awaken the same technique in both of their eyes but eventually goes blind. Use of the dōjutsu gradually deteriorates the user's eyesight to the point of blindness; a harsh fate for those that have grown accustomed to the power and visual acuity it affords. Only by transplanting the eyes of another Uchiha can the user regain their sight and ocular powers. By transplanting the Mangekyō Sharingan of an Uchiha with strong blood ties to the recipient — ideally a sibling — an Eternal Mangekyō Sharingan can be created. This process takes several days for a complete recovery and not only permanently restores the recipient's eyesight, but also bolsters their own ocular power with that of the donor's, signified by the intertwined appearance of their Mangekyō Sharingan's tomoe seals. Due to the compatibility issues and the Mangekyō Sharingan's rarity, not everyone can gain these benefits by transplanting the eyes of just any Uchiha, which has been the cause of many fruitless sacrifices throughout the Uchiha clan's history. Thus far, only Madara and Sasuke are known to have been successful in this endeavour.
