Shiro

Shiro is a childhood-friend of Ganta. She has two personalities, herself and the Wretched Egg

Personality
Shiro is a bubbly, happy girl that seems to be a klutz. She also has a lot of energy (most likely from the fact she eats nothing but sweets), although her mind cannot understand much. While she doesn't fully understand Deadman Wonderland, she knows how to help Ganta and only wants his happiness- even to the point of killing him when he asked. She is incredibly strong, however dense she is, and uses her strength to help Ganta as much as possible after a childhood incident between them. During the dog race show, she's seemigly oblivious to the dangers of the game and occasionaly gets in the way of Ganta's progression (or survial) only to be later realised by Ganta that she was discreetly taking Ganta's blows for him.

History
Before the birth of the Wretched Egg, Ganta and Shiro played quite often, sharing a common admiration of Ace Man, a Megaman-like cartoon hero. Shiro was a test-subject of Ganta's mother, so they saw each other often. She got along well, but one time, when Shiro was in grave pain because of the constant injections, they once bickered so violently that Ganta took his toys and ran away from the hospital. Soon after, he came face-to-face with a rabid, vile dog. Ganta dropped to his knees in fear and called for Ace Man to save him. Suddenly, Shiro appeared in between Ganta and the dog, saving his life. After this, Ganta and Shiro were even more close. She was used in nanomachine expirements that led to the creation of the Wreched Egg and Nameless Worm-Nanomachines she seems to be able to produce. As shown her body has been ripped apart several times possibly when her limbs were removed multiple times to create the Chorus Blocks.

Some time after that, Hagire built Deadman Wonderland and built a room for Shiro, supplying her with all the candy she ever wants.

Prison arc
Shiro is first seen sitting on the roof of Deadman Wonderland, singing the Woodpecker Song. Somehow, it seems she smells Ganta arriving at DW.

In the manga, she and Ganta first reunite when Shiro jumped through Ganta's cell window, breaking the bars in the process. She heard Ganta saying he wanted to die, so now she wants to help him die. She held a piece of broken glass and attacks him with it.

Abilities
Branch of Sin: As Shiro, she has shown minimal control of her Branch of Sin and has been able to use it in combat only once. She first discovered her powers when Ganta and Senji were discussing their Branches of Sin. She used it to fight for the first time in Ganta's battle with Shishito Madoka, where she saved Ganta when he was about to get killed.

Trivia

 * Shiro's name means white in Japanese.
 * Shiro is the only character so far that has appeared on multiple volume covers: Volume 1 and 2.