Mary

Mary is a modified human who serves the Union as a member of its Assassination Squad, where she was partnered with Jake. She was the first female modified human shown in the series and one of the earliest antagonists.
Mary is among the first female experiments seen in the series. She is one of the highest-ranked and most powerful successful experiments created by Dr. Crombel. The Union's assassination unit consists of her and Jake. It is implied that Mary is more powerful than her partner, meaning she holds a higher rank and commanding capability.
Although quiet, Mary is very intelligent and loyal to Dr. Crombel. She rarely displays emotion, which frequently annoys Jake, her partner. She has a very cold and cruel nature and always strictly follows her missions. When she died, everyone in the Union, including the members of the DA-5, showed surprise. They all found it hard to believe that she could have been killed.
She has been shown to have the ability to transform her arms, and in this transformed state, she gains immense speed and strength. It is implied that she is even more powerful than Jake, as he had vowed to kill her and Dr. Crombel one day, but not until he became stronger. Jake is also afraid of her, further attesting to Mary's immense strength.