Fishbone D

is a Hollow who attacks the Kurosaki Clinic on the night Ichigo meets Rukia. He is subsequently purified by Ichigo, after the latter receives Rukia's Shinigami powers.

Appearance
He is a Humanoid Hollow, approximately 16ft in height, with a fish like mask and a dorsal fin on his back. His shoulders and arms are plated with what appears to be a part of his mask and his body is covered with dark gray stripes, resembling the scales of a fish.

Agent of the Shinigami arc
Fishbone first appears when he chases down and devours the Plus of a little girl, who was a friend of Ichigo, and haunted her death spot, near Ichigo's home. He was being followed by a Shinigami, Rukia Kuchiki, but she unfortunately had her senses blinded by Ichigo's vast Reiryoku and lost his tracks. After killing the Plus, Fishbone makes his way to the Kurosaki Clinic, where he crashes through the kitchen wall and attacks Ichigo's father, Isshin, and his younger sister, Karin. He then grabs Karin's twin sister, Yuzu, and takes her out of the house.

Yuzu's cries attract the attention of both Ichigo and Rukia. Ichigo soon runs out of the house, wielding a baseball bat, but Fishbone effortlessly punches him away, breaking the bat. When he is about to strike again, the Fishbone's arm is suddenly sliced by Rukia, which causes him to drop the Human girl before retreating into Hueco Mundo for several seconds to heal his wound. When he returns to the Human World, he spots an opportunity to strike at the Shinigami and seizes it, knocking her against a wall. Seeing this, Ichigo stands up to Fishbone and challenges him. Fishbone attacks, but the Shinigami blocks him with her own body, her Zanpakutō cutting into the upper part of his mask, prompting him to retreat again. When he returns, Fishbone attacks again, but when he nearly reaches his targets, Ichigo is suddenly turned into a Shinigami and cuts off Fishbone's arm. Fishbone makes the mistake of attacking again without retreating, which proves to be fatal when Ichigo cuts off his leg and then through his head, purifying him.

Powers and Abilities
Spiritual power: Fishbone D has a sizable spiritual power. When Rukia exits the area being effected by Ichigo's spiritual pressure, she is astounded by the sudden amount of spiritual pressure Fishbone D is emitting.

Trivia

 * Fishbone D's name was only revealed later on, when Rukia attempted to collect the bounty for his purification.