Rukia died as an infant and was sent to Soul Society with her older sister, Hisana. Though Hisana initially tried to protect and provide for Rukia, she could not ensure her own survival while caring for a baby as well, and thus abandoned Rukia. As Rukia grew up she befriended Renji Abarai, and over the coming years the two stayed together and looked out for one another. Once they entered the Soul Reaper academy, Rukia was adopted into the Kuchiki familyHisana, having years earlier married into the family and subsequently died of an illness, begged her husband, Byakuya Kuchiki, to find Rukia. Disgusted with herself for abandoning Rukia, Hisana wanted her sister to be part of the Kuchiki family while never knowing of their relation to each other. After succeeding in this task, Byakuya kept his word, treating Rukia as a sister and keeping his wife's secret until the end of the Soul Society arc, where he finally tells Rukia about Hisana's past.

When she was accepted into the 13th Division, Rukia's abilities made her a prime candidate for a seated position. Wishing to keep Rukia out of harm's way, Byakuya used his influence as a captain to make her ineligible for such a position. In time, Rukia befriended the lieutenant of her division, Kaien Shiba, and trained under him. During the course of a mission Kaien was possessed by a hollow and Rukia was forced to kill Kaien to protect herself. While dying, Kaien apologized to Rukia for allowing himself to be possessed and thus putting her in that positionRukia returned his body to his family, though could not find the courage to tell them how he had died until she learned about His

Renji 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, the number of tattoos on his body increase as well, starting from his early days as a Soul Reaper candidate until when he becomes Byakuya Kuchiki's lieutenant (at this time his tattoos now cover his entire back). These tattoos match those of Zabimaru in its manifested state. He dresses in the standard Soul Reaper outfit, though he usually includes some sort of elaborate headgear (usually expensive-looking glasses or a white headband). 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

As far as his personality goes, Renji is about as eccentric as any other Soul Reaper. 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. 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 similar to Ichigo Kurosaki in many aspects, and the two are mistaken for brothers in the anime's Bount arc. Ichigo claims they are cousins to keep things simple, allowing many hilarious situations to occur later, including comments over their unusually colored hair. A continuing gag in the series is Renji's nick name, red pineapple, referring to his crimson hair kept in a pineapple top-like ponytail. During a filler arc before the invasion of Las Noches, Renji wears a shirt with 'Red Pineapple' printed on the front, supposedly bought by Ichigo Kurosaki as a joke.