Renji is quite dynamic. His personality varies from smug and cocky to disquieted and depressed after a major defeat, but shows himself to be an incredibly serious and determined fighter when confronted with an actual threat. Willing to fight, kill, and die for whatever he believes in, Renji is a dangerous man to those who stand in his way. compares his fighting style to that of . Renji is determined to surpass his captain, , and it's this determination that drives Renji to grow stronger. Renji likes (a popular fish-shaped pancake usually filled with sweet bean paste), and has a dislike for spicy food. Renji also likes , and in his free time works on assembling a team from the 6th Division, with success, more or less. The current members are himself, , and the 4th, 8th, 13th, and 20th seated officers.
All of Renji's sunglasses are purchased from 's popular store and cost half a year's worth of his pay check. However, every time he wears a pair, they are broken in one way or another. On these occasions, he replaces them with a tied white bandana, until he can purchase a new pair of goggles. His dream is to wear a pair that he himself designed at least once.
Renji grew up in the 78th District of , , with several other children. Having come to alone, they helped each other to search for their families. One day, after stealing a jug of water, Renji and his friends were chased by a kama-wielding adult. tripped the adult and urged Renji's group to follow her to avoid losing the water. Rukia joined their group and they lived together as a family. They all hated Inuzuri and the people there. Renji disliked the fact that Rukia had spiritual power like he did. Ten years after Rukia joined their group, with all of their friends dead, Rukia proposed that they become , which Renji agreed to do. As they were quite gifted with spiritual powers, they entered the with ease, where they struggled to prove their worth among those from . The night before the welcoming ceremony for the new students of the Academy, Renji slept in a tree, against Rukia's advice. The following morning, he fell out of the tree and landed on a headstone where a startled had been praying. Having scored among the highest grades in the entrance exam, Renji was admitted into the top class along with Izuru and .
Renji helps to defend .
Two months after entering the Academy, Renji scolded Rukia for still not fitting in and informed her that he was going to the for field training to practice the for the first time. Whilst being briefed on the field trip by , , and , Renji failed to recognize Shūhei, who was to lead the mission. Izuru explained to him that Hisagi was famous and a gifted student. Renji, Izuru, and Momo were assigned to the same group. When Momo joined them, Renji kicked Izuru because of how he greeted her, saying that he should not let his emotions show so easily. While in the Human World, Renji remarked that Konsō was a lot easier than he had imagined. He then lost his temper with the constantly fidgeting Izuru and punched him. As Shūhei called an end to their field trip, the group was attacked by a , which killed Kanisawa and seriously wounded Aoga. Shūhei ordered the group to retreat while he stayed to fight the Hollow. When a second Huge Hollow appeared, Momo stopped and questioned why they were running away. Renji reminded Momo that the Hollow had just killed two sixth year students. When Momo rushed back towards Shūhei, Renji and Izuru followed her and helped to block the second Hollow's attack on him. When more Huge Hollows showed up, they were saved by the arrival of 's Captain , and his lieutenant, . When Momo wondered if they would ever become as strong as Aizen and Ichimaru, Renji laughed at the notion and insisted that captains and lieutenants were monsters.
Renji and Rukia during their days.
Having passed an important exam, Renji rushed to find Rukia to tell her. However, when he found her, she was with several Shinigami, including . As they left, Renji noted Byakuya's power, causing him to wonder who he was. Renji asked what they wanted and congratulated Rukia when she told him that they want to have her adopted into the , have her graduate immediately and assigned to the . Rukia thanked him and left. Renji told himself that Rukia finally had a family and that he should stay out of it. After Rukia left, Renji trained every day in a bid to beat Byakuya, but he was unable to defeat him even once.
Renji graduated from the Shin'ō Academy in its 2,066th year and joined the Gotei 13, where he initially served under Aizen in the 5th Division, along with Izuru and Momo. The rebellious Renji, however, was moved to the and rose to the rank of 6th Seat. During his time in the 11th Division, he befriended , to whom he revealed that he wanted to become stronger than Byakuya Kuchiki. Ikkaku taught Renji how to fight and Renji became aware that Ikkaku had a Bankai, and requested that he use it to train Renji.
Forty years after Rukia's adoption into the Kuchiki Clan, in mid-April, Momo and Izuru presented Renji with a letter stating that he was to be promoted to lieutenant of the 6th Division. He formally accepted Momo's words, which caused her to tell him not to be so uptight. Ikkaku told him that he was now a step closer to Rukia and that his will has been strong for forty years, but now that he was a lieutenant, they should return to the type of relationship that they once shared. Izuru informed Renji that Rukia was leaving on a mission to the Human World that afternoon. When Momo urged him to hurry, Renji told her that he would wait until his promotion was made official a month later, and that when she returned, he would surprise her with it. On the 19th of July, Renji was sent alongside his captain to arrest Rukia and return her to Soul Society.
