Penumbra was an assassin who once served under the League of Assassins.
Mio was a simple hearted girl who lived in the village of Manpur Tapara, where the secular Shihan Matsuda also lived. Mio often sharpened Sensei Matsuda's blades, becoming skilled with them as well. Her skill attracted the attention of Ra's al Ghul, who further trained her to be an assassin. When Sensei Matsuda took in an apprentice, Bruce Wayne, Mio found herself attracted to him and the two became lovers.
However, Shihan's wife eventually contacted the League to get Shihan killed. Ra's assigned Mio to the task, and while she completed she was met in combat by Bruce. Easily defeated, Mio was speared by falling glass and presumed dead by Bruce. In truth, Mio had simply slowed down her heart rate, giving her time to escape. When she returned to Ra's he bestowed upon her the power to control shadow, an ancient Indian Martial Arts technique.
The world and herself, Mio became Penumbra. This was in accordance to being able to grow extra arms out of shadow with her new power. In 2013, Penumbra was contracted with killing the president of Bhutan in Gotham City. However, after being delayed by Harper Row, she was met by the infamous Batman who reminded her of her past as Mio. After falling off a ledge, Penumbra disappeared, her mission a failure, resulting in her being punished by Ra's.