Sharingan

“My rage is derived from eyes so sharp they see through the idiocy being passed off as sophistication. Under the cloak of universal themes and terms such as freedom, change, and acceptance, madness ensues, being readily welcomed by those whose mind's eye questions nothing.” -Justin K. McFarlane Beau

Capabilities
The Sharingan is unlocked when an Uchiha feels a massive rush of emotions which trigger a rush of chakra through the optic nerve which transforms their eyes into the Sharingan. It is the same with its upper evolutions. Once someone has reached the Mangekyou Sharingan they unlock the Susanoo and when they transplant the eyes of their siblings that have the Mangekyou Sharingan they unlock the Eternal Mangekyou Sharingan. Users of the normal Mangekyou Sharingan have access to a few abilities. If said abilities are overused they can lead to blindness. So does the Susanoo.