Arnold is Reimi Sugimoto's dog and, like her, is a Ghost residing in Morioh's Ghost Girl's Alley. As another victim of Yoshikage Kira, he remains by Reimi's side awaiting the day their killer is brought to justice.
Arnold is a large dog with light fur, seemingly of the Labrador retriever breed. As a ghost, he has a huge gash across his throat from when he was killed by Kira that constantly drips blood.
As a guard dog, Arnold is strong and fierce to his enemies. However, he is friendly to strangers, as he didn't attack Rohan and Koichi when they stumbled into the alley. Loyal to his master, he remains by Reimi's side even in the afterlife.
Arnold was Reimi's guard dog 16 years prior to Diamond is Unbreakable. One night, Yoshikage Kira invaded their house and slashed his throat. Picking up the dog's dead body, Kira hanged him on the clothes hook in the wall, his neck almost cut off. His blood remained dripping for more than 10 minutes before anyone noticed his death. Living as ghosts bound within a ghost alley, Reimi and Arnold await the day they can find someone to hear their story and report Kira to the police before more girls are killed.
Diamond is Unbreakable
Reimi and Arnold finally find someone with a supernatural ability who can see them: Koichi Hirose and Rohan Kishibe. After hearing their story, they agree to help after learning the killer is still alive, and they warn the Stand users of Morioh. Arnold remains by Reimi's side as she bides her time in the alley.
When Kira dies, his soul is transported to the ghost alley. When he attacks Reimi, Arnold defends her by biting Kira's arm off, causing him to look back and be dragged into the afterlife by hundreds of hands. Finally at peace, the ghost alley disappears, and both Arnold and Reimi ascend to Heaven.
Chapters / Episodes
- The story Reimi tells about the night of her death bears a similarity to the The Licked Hand urban legend, in which the protagonist also finds her dog hanging in a closet with its throat slashed.