Black Hayate

Black Hayate (ブラックハヤテ) is Riza Hawkeye's pet Shiba Inu puppy. He was found on the street by Master Sergeant Kain Fuery who - due to the fact that his dorm wouldn't allow him to keep a pet in house - tried to find the little dog a good home among his comrades, but to no avail: Vato Falman also lived in a dormitory, Heymans Breda's intense fear of dogs prevented him from even coming close to Fuery while he had it with him, Jean Havoc made a joke about dogs being a delicacy in Xing and was deemed unfit for pet ownership, Edward Elric explained that he and his brother were unable to care for a puppy because of their constant traveling and Roy Mustang spoke as if he would mistreat the dog and was also deemed unfit for ownership. After it became clear that the dog would have to go back out into the rain, Lt. Hawkeye offered to take the dog, which she names "Black Hayate" (Black Hurricane) to the dismay of her comrades. Though, immediately after Fuery hands the dog over to her, it urinates on the floor in the Eastern Headquarters, prompting Hawkeye to implement her own brand of tough love: housebreaking by gunfire.

In the manga
Black Hayate next appears in Chapter 37, keeping Master Sergeant Fuery company during the stakeout of the "Fishing Mission". When Hawkeye is attacked by Gluttony, Hayate leaps into action to protect her and is followed by Fuery, displaying uncommon sense by biting the Homunculus in an area he couldn't reach and by adeptly dodging out of the way of Hawkeye and Fuery's gunfire. Hayate also displays high obedience by following Hawkeye's command to stay with Fuery as she and Mustang go to chase Gluttony down, though he does jump on Edward in Chapter 58 against Hawkeye's wishes.

In Chapter 87 of the manga, after Fuery mentions that Black Hayate's ability to sense Homunculi was incredibly useful and that he should be considered a ranked officer, Mustang gives him the unofficial rank of Second Lieutenant (to Fuery's dismay, as the dog now outranks him).

In the epilogue of the last chapter, a picture shows Hayate has mated with, apparently, a white Shiba Inu and has gained three puppies.

Anime
After his adoption, Black Hayate becomes very disciplined under Riza's care, having to sit, shake (With one paw and then the other), and lay down before being allowed to eat. Black Hayate apparently likes to bury bones within the old execution grounds near Warehouse 12, as seen in episode 37.

Trivia

 * Like members of the military in the series, Black Hayate is named for a military vehicle - the Nakajima Ki-84 Hayate fighter plane.
 * During the The Flame and The Fullmetal show (a fan video created by Vic Mignogna and Travis WIllingham using FMA action figures that is showed at anime conventions.) Edward is seen drawing a crayon doodle of Black Hayate which he then drops in a blender and tricks Roy into jumping in after it.
 * In the Chibi Party OVA, it is revealed there is a team of Black Hayate who run over Ed and Al. This being a gag referring to the use of multiple animals to play the part of one in most live action series.
 * Black Hayate came in 23rd place in a recent fan poll, a spot he shares with Lust.
 * In the Gaiden "Flame Alchemist", Roy Mustang is caught slacking off from his work while drawing a doodle of Black Hayate.
 * The author seems to like making jokes about Hayate and his relationship to other characters, especially Riza. There are several omakes regarding Hayate's thoughts and devotion to his owner.