Pluto

Pluto (プルートゥ, Purūtu), nicknamed Plu-Plu, is a demon hound that the Phantomhive household picks up in the anime.

Character Outline
In his human form Pluto has shoulder-length silver hair, red eyes with slit pupils, fangs, and black toenails. He is often shown nude in his human form, since he frequently changes back and forth from his human form to his demon hound form. Eventually, he wears a suit.[1] In his demon hound form he becomes a immense and monstrous dog with white fur.

He never speaks, and simply makes dog-like sounds, such as howling, barking, and whining noises. Even in his human form, he retains dog-like characteristics, such as continuing to run around on all fours and using his nose to find things. He can turn into his human form upon will, or unintentionally when excited.[2]

Pluto does not seem to be overly fond of most people, but listens to Sebastian Michaelis most of the time and is notably envious when Sebastian gives his attention to a cat.[3] He likes Innuko dog treats.[1]

Houndsworth Saga
When the Phantomhive household goes to the village of Houndsworth, they initially believe the legend of the Demon Hound to be a farce created by Henry Barrymore, but when he is dragged from the cell where he was being kept and found dead, they investigate further.[4]

Finnian, Baldroy, Mey-Rin, and Tanaka, while looking for Angela Blanc, initially discover a strange, nude man, and before they can investigate him further, they are distracted by the townspeople. When they turn around, they see a large Demon Hound, but decide to follow him further when they notice he is carrying part of Angela's clothing. However, it turns out that he was just her pet, but had killed Henry because of his abuse of the Demon Hound legend. Angela asks if they will take him in so he can behave better, and Ciel Phantomhive agrees, knowing how much Sebastian despises dogs.[5]

Shard of Hope Saga
He aids Ciel, Grell Sutcliff, and Sebastian in finding Elizabeth Midford by unsealing the door to the tower she is being held in. After their fight with Drossel Keinz he is seen calmly laying at Drossel's master's feet, much to Ciel's and Sebastian's surprise. It is later shown that the reason for this is because the puppet manipulating Drossel was controlled by Angela.[6]

Conspiracy and Revenge Saga
Pluto is seen when Mey-Rin, Baldroy, and Finnian recall their pasts and how they were recruited.[7] He is seen helping Finnian with his garden work, though he creates more problems by burning all the trees. Later, he uses his fire breath to defend Phantomhive Manor. When Ash goes on the rampage, he uses Pluto's demon hound abilities to set most of London on fire. As he goes out of control and cannot be stopped with mere anesthetic, Ciel orders his servants to kill Pluto. Mey-Rin, Finnian, and Baldroy sadly agree, and using their various skills, are able to take him out, injuring themselves in the process.[8]

In the end Sebastian promises Ciel that he would "gather Pluto's bones" later, indicating that Pluto had been killed.

Background
Pluto is Tien Shinhan's and Chiaotzu's pet demon hound and a powerfull fighter.

Supervillain Yamcha Saga
Pluto fights alongside Yamcha against the Z Fighters in his Etherious form. In this form he rivals the power of Super Saiyan Blue Vegeta. After he was defeated by Goku he says this new power will be usefull in the upcoming Tournament of Might.

Hell Gates Saga
Pluto is seen sleeping in Hell and he doesn't realise there is a battle right in front of him. He wakes up at the end of the battle and asks Tien what is going on with the latter punching him in the head.

Universe Survival Saga
He is chosen as one of the ten fighters for the Tournament of Might for the fate of Universe 7. Etherious Pluto eliminates Nink of Universe 4. Chengi later steals his body and kills him.

Conspiracy and Survival Saga
He was wished back to life by Dragon balls and lets Gohan absorb him in order to beat Saiko. Then he gets saved from the erasure by Zen-oh as Wolfy writes him off.

List of Characters killed by Pluto

 * Houndsworth inhabitants - Hundreds of cut of limbs were found close to the cemetery.
 * Henry Barrymore - Dragged out of his cell and killed.
 * London inhabitants - Pluto set whole London on fire and killed many people.