Tomoo

"This is the first time I've seen you so upset. Cry! Cry and beg! If you don't...we'll have to hurt the dog instead of you."

- Tomoo forcing Lucy to show some emotion, because if she won't they'll be forced to torture her puppy instead of her.

Tomoo is a minor, but significant antagonist in the anime and manga series Elfen Lied. Tomoo served as the chief force that ultimately turned Lucy into a homicidal maniac, and he's also the reason for her deep hatred of humanity.

Biography
Tomoo was an eleven year old boy who was the ringleader of a group of nameless bullies. His favorite victim was Kaede. He and his acquaintances endlessley taunted her and bullied her because of her bottling up her emotions, and called her names such as "Oxen" because of the horns on each side of her head. Tomoo mainly targeted Kaede, because he wanted to see her express some emotion from all of his attacks.

One day, Lucy meets a young girl at the orphanage, and befriends. It's unknown if the girl befriended Kaede because she genuinely felt sorry for her, or if Tomoo set her up. Whatever happened, the girl tells Tomoo that Kaede had a puppy that she was taking care of, and the other boys present Tomoo with the puppy. Tomoo then teases Lucy about the puppy, and then proceeds to throw it hard against the wall. He then grabs a vase, and then beats the poor dog with the vase and continued to do so until the poor animal stopped moving. Kaede had finally had enough of her tormentors, and she proceeds to use her invisible vectors on them, and she slaughters them all. Tomoo was the last one that was killed.

The influence that Tomoo had on Lucy continued even after he had died. Tomoo would often be manifested up by Lucy whenever she felt great stress. He would always be mocking her and calling her names. Ultimately, Tomoo is the one who was responsible for Lucy's descent into madness, and he was the one who molded her into a serial killer because of his influence.

Personality
Tomoo was considered a very cruel and monstrous figure. He killed the dog knowing that it would destroy Kaede, because that dog had served as her only friend during her miserable existence. He's also a very sadistic individual; When he was killing the puppy right in front of Kaede, he's shown clearly sporting a look of sadistic glee on his face. These traits most likely would've made Tomoo become a serial killer had he grown up if Lucy didn't kill him out of anger for him killing her pet.

Trivia

 * Tomoo, alongside with his companions, are very similar to Chris Hargensen & Billy Nolan as both bullied the protagonist for fun thus turning them into psychopaths, one of them directly killed an animal, both their victims are psychics, both are later killed in a gruesome death by the protagonist's power as a revenge & both appear as hallucinations in the protagonist's mind, particularly in the 2002 version.
 * Tomoo is also very similar to Henry Evans as they are roughly the same age, males, dog killers (done for fun), and target a specific young girl they enjoy torturing.
 * Even though he is a minor villain, Tomoo can be considered as one of the most hated Elfen Lied villains ever due to his cruel & inhumane treatment towards Lucy, possibly more than his companions & Elfen Lied's main antagonists Director Kakuzawa and the Unknown Man who are far more evil and sadistic.
 * Much of the fanbase believes that if Lucy had never killed Tomoo, he would have likely grown up to be a serial killer possibly worse than Lucy herself since killing an animal is said to be the first sign of a serial killer.
 * Even thought Tomoo is a kid, many viewers stated that he deserved that kind of gruesome death.
 * On the flip side of the previous two statements, controversy has arisen between fans, viewers and critics of the show regarding Tomoo as many do not believe that a child of his age can be as evil as he was.
 * Additionally, Tomoo likely suffers from sadistic personality disorder, a mental condition that causes people to be sadistic towards others. The disorder is treatable, however, the younger the person is, the easier they are to rehabilitate. Surprisingly that means that given the proper mental hospital environment, the proper psychologists, Tomoo and his allies might have had a shot at rehabilitation had they been taken to a mental ward.
 * Tomoo is voiced by Christopher Patton in the English version, who also voiced the English versions of some notable anime villains such as Greed & Turles.
 * In the Japanese version, Tomoo is voiced by a woman.
 * Tomoo's character is very similar to that of Kakihara from Ichi the Killer, as well as his homage Chaka from Black Lagoon, notably their inhumane brutality.
 * Tomoo, alongside his companions, are slightly similar to the Unknown Man, another hated villain in the same series. Both are animal abusers, violent sadists, both are highly regarded as a Complete Monster, both have their vile actions revoked another villain, both are killed by the same person via decapitation & both are one of the most hated villains in the series. It can be hinted that Tomoo might ended up being like the pedophile mercenary if Lucy have not killed him and his companions in the first place.
 * He was erroneously given the name Tomohiro in the original ADV credits.