This Article Contains Spoilers - WARNING: This article contains major spoilers. If you do not wish to know vital information on plot / character elements in a story, you may not wish to read beyond this warning: We hold no responsibility for any negative effects these facts may have on your enjoyment of said media should you continue. That is all.
Shiro, also known as the Wretched Egg, is the secondary antagonist/deuteragonist of the manga and anime series Deadman Wonderland. She is the source of the Branch of Sin virus, making her responsible for the existence of all Deadmen.
Shiro is the artificial daughter of Hagire Rinichiro who was infected with a mysterious virus that gave her abilities which was being researched by Sorae Igarashi, whose son Ganta the girl befriended. However, as years passed, Shiro suffered horrific human experimentation to have virus evolve into the Branch of Sin strain. Though she became the first Deadman, Shiro's ordeal caused her to homicidal alter ego that became known as the Wretched Egg which caused the Great Tokyo Earthquake. Despite being the opposite of Shiro in nearly every way possible, the Wretched Egg shared her other self's affection for Ganta but from different perspectives. Though she can be subdued by a lullaby generated by Deadman Wonderland's Mother Goose mainframe, there are moments when the Wretched Egg assumes control over Shiro's body.
One such event was the slaughter of Ganta's classmates and giving Ganta his Branch of Sin. Later, Ganta ends up being framed for the massacre and sentenced to Deadman Wonderland where he is greeted by Shiro despite his inability to remember her at first. During that time, the Wretched Egg persona surfaced a bit times with Ganta unaware of at the time. Eventually, the Wretched Egg persona integrates back into Shiro once the Mother Goose system's lullaby no longer represses her and reveals to Ganta that her actions against him were so that he, the one she loves, can be the one to end her misery.
The two battled (with Ganta unable to bring himself to kill her), which caused the whole prison/theme park to crumble into the ocean, resulting in a draw. She was sent to a mental hospital afterwards.