Karyuudo's Attack Dogs are minor characters from Future Diary. They are dogs raised by Karyuudo Tsukishima, trained to be vicious killers. When he entered the Survival Game, he used these dogs to attack the other competitors.
In addition to being fast and powerful animals, Karyuudo's dogs are outfitted with metal augments to improve their biting attacks. In the manga, Karyuudo's dogs wear large metal mouthpieces; in the anime, their teeth are fitted with serrated metal devices resembling braces. Each and every dog apparently has a tracking device on them, allowing Karyuudo to monitor their positions on a large computer in his house. He also has at least one dog fitted with a speaker collar and listening device to help keep tabs on the situation.
When his dogs are sent into the field, Karyuudo divides them into teams with military designations (Alpha-1, Alpha-2, etc.). This allows him to coordinate them like an army, sending teams to attack directly, flank their target, or lie in ambush. It is unclear if Karyuudo did this before he gained his Future Diary, or if the item helps make the dogs easier to command.
Controlling the dogs is expedited by Karyuudo's Breeder Diary, a Future Diary that tells its user what the dogs are seeing. This allowed Hinata Hino (using the Diary on her father's behalf) to know when the dogs had lost the others despite not being in visual range. The Breeder Diary's effectiveness is limited by the number of dogs it's tracking at once; the more dogs there are, the harder it is to keep track of them all. Karyuudo circumvented this by using his computer to help keep track of the dogs' positions, allowing him to focus on what they were seeing instead; Hinata got around the Diary's weakness by focusing her commands on one team of dogs, telling all the other teams to follow their lead.
Like the rest of Karyuudo Tsukishima's dogs, the attack dogs were painstaking raised and cared for in the Tsukishima estate. Karyuudo spared no expense to give his pets the most luxurious experience possible, even training them to sit at a long dining table while he served them steak and fine wine; on the other hand, this caused him to neglect his daughter, Hinata Hino, and even himself.
When Deus Ex Machina begins the Survival Game, Tsukishima prepares for the hunt by readying his attack dogs. Around the end of May, with four participants killed, he decides to target Aru Akise after noticing the youth lurking about outside, suspecting him to be one of the other diary holders. Realizing that commanding his dogs directly could expose him to danger, Tsukishima has the idea to loan his Breeder Diary to his daughter, Hinata Hino, and have her command the dogs on his behalf.
To attract his foes' attention, Tsukishima uses his dogs to stage a number of serial killer-like murders, creating a similar public scare like that of the late Takao Hiyama. The dogs' work on their victims was at best horrible, devouring parts of their victims' bodies and leaving the remains for the police to find. Learning that Yukiteru Amano was set to start his new term at Umesato Elementary School - the same school as Hinata - Tsukishima lent his Breeder Diary to Hinata, instructing her to use his attack dogs to help him win the Survival Game; in return, he would use his powers as God to make up for neglecting her in the past.
Upon meeting Yukiteru, Hinata suggests investigating the sites where her father's dogs had killed people. Yukiteru agrees, accompanying Hinata, Mao Nonosaka, Ouji Kosaka, and Yuno Gasai to the park where they find one of the crime scenes. Hinata runs off ahead and fakes her death, using a fake arm to make it look like she had been torn apart by Karyuudo's attack dogs; from here, she began sending teams of dogs to attack her friends.
With the help of an arriving Akise, Yukiteru, Yuno, Mao and Kosaka fled to a nearby building; there, they managed to fend off the dogs by following the instructions on Yuki's diary. With the dogs pinning them down in the building, Hinata personally enters to claim Yukiteru's phone with the help of her accomplice, Mao. In the ensuing confrontation, Akise tricks Hinata in a coin-toss game, Mao is stabbed by Yuno, and Yukiteru, Yuno, Akise and Kosaka manage to flee outside; an enraged Hinata orders all of the attack dogs to chase them.
After evading the dogs once more, Yukiteru returns with the intention to save Hinata, noting that she promised that they could all leave as friends if she failed the coin toss game. Yuno charges in first, taking Hinata at knifepoint and threatening to kill her unless she calls off Karyuudo's dogs and surrenders the Breeder Diary. Yuki manages to calm Yuno down by declaring to his friends that she is his girlfriend, allowing Hinata to be spared.
Hinata laments failing her father, but one of the dogs arrives with an attached voice speaker that allows Karyuudo to address her. Having been monitoring the action all along, Tsukishima apologizes to Hinata for mistaking Akise for a diary owner, revealing that his role in the game is over. Hinata asks about his promise, but Tsukishima apologizes again and reveals it was a lie; in the anime, he openly laughs at Hinata's naivety and his own promise. Tsukishima criticizes Hinata for her naivety, but tells her not to become a bad person like he became. Clutching a family photo of himself, his wife and a young Hinata, Tsukishima informs Yuki to beware of the diary owners who act nice, but can also be deceptive - moments later, he was shot dead by Keigo Kurusu.
It is unclear what became of Karyuudo's dogs after his death, but they presumably died from neglect or during the collapse of the second world.