Renji Abarai came from the 78th district of Rukongai and grew up as an orphan with several other children, including Rukia Kuchiki. The company of children lived by stealing or hunting for food. Though Renji and Rukia quickly discovered they had spiritual powers, they remained with their friends until they all died off, which prompted them to become shinigami for a better life.
At the shinigami academy, Renji was admitted into the top class, being very adept at swordsmanship, although quite inept at kidō. His senpai was Shūhei Hisagi. At the academy, Renji befriended Izuru Kira and Momo Hinamori, who each proceeded to become lieutenants. His relationship with Rukia became distant after her adoption by the Kuchiki family since he felt he had no place interfering with her life now that she was a noble, despite the fact they both seemed to regret losing the company and confidence of the other.
Renji, Kira and Hinamori served under Sōsuke Aizen and Gin Ichimaru in the 5th division, after which Kira and Hinamori (the loyal ones) were put under Ichimaru and Aizen in the 3rd and 5th divisions respectively. The rebellious Renji was moved to the 11th Division and eventually rose to the 6th seat.
Renji is one of the more unusual characters in Bleach in terms of his appearance. He has long crimson hair, usually kept in a high ponytail, and his entire upper body is covered in tribal tattoo work. How he got these tattoos is unknown, but it appears that with every achievement Renji attains, his tattoos increase as well, starting from his early days as a shinigami candidate until when he was imprisoned by Byakuya Kuchiki (his tattoos cover his entire back at this point of time). He dresses in the standard shinigami outfit, though he usually includes some sort of elaborate headgear (usually expensive-looking glasses). All of Renji's sunglasses are from Seireitei's popular "Silver Dragonfly Glasses Store" and cost half a year's worth of his paycheck. Unfortunately, every time he wears a pair, they are broken in one way or another (usually in a fight with Ichigo).[1] He likes taiyaki (a popular fish-shaped pancake usually filled with sweet bean paste) and dislikes spicy food.
As far as his personality goes, Renji is about as eccentric as any other shinigami. He varies from smug and cocky in his first appearances to downright angsty and depressed after his major defeats, but shows himself to be an incredibly serious and determined fighter when confronted with an actual challenge. Renji harbours deep affections for Rukia Kuchiki. This is proved numerous times throughout the story, particularly during his flashback of his youth with Rukia in Rukongai. Willing to fight, kill, and die for whatever he believes in, Renji is a dangerous man to those who stand in his way. He is much like Ichigo Kurosaki in many respects, and the two are mistaken for brothers in the anime's Bount arc. Ichigo claims they are cousins to keep things simple in that instance.
During his time in the 11th Division, he befriended Ikkaku Madarame, who taught Renji how to fight. On the same day Rukia headed for the human world, Renji was promoted to lieutenant of the 6th Division.[2] After meeting Byakuya Kuchiki, the 6th Division's captain, Renji's greatest dream has been to surpass him in strength.