Akamaru

In the first part of the story Akamaru is a small pup with white fur, brown-tipped ears, a brown nose, and a brown outline around his mouth, resembling a Great Pyrenees and usually riding on Kiba's head or tucked inside his jacket. His eyes stay narrowed to near-slits, and the fur on his crown stands up in a rough mohawk. When he swallows a soldier pill his coat flushes red and his temper turns feral, the very trait that gave him his name.

By the second part he has filled out into a large adult dog, big enough for Kiba to ride on his back, though his features are otherwise unchanged. Years after the Fourth Shinobi War a few wrinkles gather on his snout, the only real sign of age.

Databooks describe Akamaru as lively and loyal, and both traits show in how he lives alongside Kiba, the two forever running and chasing one another through the trees. The moment Kiba is hurt in a fight, the dog races to him. A story told from Akamaru's own perspective reveals a wry, self-correcting mind and a blunt, almost scientific view of people; he thinks humans waste their prime chasing mates instead of sharpening their skills, and he grows fussily protective when Kiba falls for Tamaki. In the epilogue he has aged into a contented dog who naps through the day, plays with his pups, and smirks knowingly at his master.

Akamaru's senses far outstrip an ordinary dog's, and paired with Kiba's ability to talk with him they make the two superb at gathering and trading information; he can even read chakra through his nose to gauge an enemy's strength. In combat he often takes Kiba's shape with the Beast Human Clone technique to launch spinning Passing Fang strikes, and the pair can fuse into a giant two-headed wolf for a devastating Fang Wolf Fang. Because that assault moves too fast to aim, Akamaru first marks the target by urinating on it so their noses can guide the blow. He is also handy with traps such as explosive tags.

Through Part I he helps Kiba cheat his way past the written exam, is traumatised by witnessing Gaara's brutality, and battles Naruto in the preliminaries. During the mission to recover Sasuke he and Kiba unleash their double-headed wolf against Sakon and Ukon, with Akamaru taking a grave wound to shield his partner. In an anime arc he is poisoned into a berserk, giant state, and Kiba lets himself be badly hurt to inject the antidote, noting afterward that the dog fought to avoid killing him.

In Part II Akamaru's size makes him a genuine force on the battlefield, tearing through zombies and Zetsu clones. Assigned to the Allied Shinobi Forces in the Fourth Shinobi World War, he and Kiba shred White Zetsu clones, best a reincarnated Sakon and Ukon, and later charge the Ten-Tails after Naruto shares Kurama's chakra. He falls under the Infinite Tsukuyomi with everyone else and is freed once Naruto and Sasuke end the war. In the New Era he lives out a quiet old age, dozing while a new pup and a litter of cats play nearby.