Lucy's Puppy was a small stray dog found by a young Lucy one day as she sought refuge from the rigors and wrongs she suffered at the orphanage where she spent much of her childhood.
In the series
Emotionally repressed around people due to the poor and sometimes horrible treatment she received at the hands of others, Lucy was unreserved around the pup and was often emotionally comforted by it when she was low. She took great care to keep the pup a secret from her tormentors and everyone else, and she would share her food with it and take it around the grounds. On some occasions, the pair would hear a younger Nozomi singing on the mountainside when she was hiding from her family. As the pup grew up, its needs and appetite increased, to the point where Lucy gave up half of her meals to feed it. Seemingly befriended by another young girl, Lucy, at last, confided in her about the pup's existence, at least in part to secure more food for it.
Whether deliberately or accidentally, the girl Lucy befriended revealed the presence of the pup to Tomoo, the ringleader of the worst of her tormentors. The gang of bullies grabbed the pup and then forced her to watch as they start hurting it. The bullies kick the pup and then proceed to brutally beat it to death with a vase, only regretting that it had died too quickly to suit their sick twisted sense of "fun." The killing of her only friend, which was likely made even worse by the possible betrayal of one she also believed to be a friend proved too much for young Lucy. Giving in to her anger, she used her vectors to tear the children present to pieces. In the process of burying the pup, she met Kouta. Sadly, the betrayals and grief from the pup's sudden and savage killing left scars that made Lucy unable to trust Kouta entirely, and when it appeared he had betrayed her as well, her murderous side was unleashed in full. Lucy never forgot him, especially during times when she felt she failed to protect those for whom she cared.
Ten years after Lucy's death, Kouta's daughter Nyuu found the jar Lucy buried at the pup's grave. Within it was a note and a jade stone, a memento of the time they spent together as children. The letter revealed Lucy's name, how much she cared for Kouta, and how much the time they spent together meant to her. The site of the pup's grave was also where the mysterious twins, who appear to be reincarnations of Nyu and Lucy, chose to reveal themselves. Like Aiko Takada, the pup was only present for a short time in the story, but posthumously, it is one of the most important characters regarding its impact, direct or indirect, on every other character.
The puppy is sometimes drawn in the series to look nearly identical to Wanta, but in other instances is drawn with streaks and spots of brown. This mistake appears to be a scanlation error wherein the pages were faded somewhat. In the pages' original format, the fur pattern is consistent.
The puppy's breed, and possibly Wanta's, might be the Yorkipoo breed. Yorkipoos are small and come in coat patterns like those of both Wanta and the unnamed puppy, and their barks are similar.
The love of a young girl for a small pup is also a critical plot point in the manga and anime series Paranoia Agent.
The actions of the bullies against the pup are somewhat similar to a sequence from Disney's now-controversial hybrid film, Song Of The South. In it, a young girl's thuggish brothers threaten to drown her beloved pup and finally take it from her. While the dog is seen in the film's final musical sequence running along with animated sapient animals, whether this fanciful sequence occurs in the real world of the film is uncertain, since much of the movie occurs through stories told by Uncle Remus. Since attacking a harmless animal for fun can be seen as typical loathsome behavior, there is no way of knowing whether this sequence could have inspired what occurred in Elfen Lied.
If the Puppy had avoided Tomoo, would Kaede have been different?