Agent Of The shinigami arc
Renji first appears with Byakuya when they arrive at the human world to arrest Rukia. Their attempt is interrupted by Uryū Ishida, whom Renji easily defeats. Ichigo then arrives to stop them, faring better against Renji than Uryū had after unlocking his hidden spiritual power. Byakuya steps in to save Renji, cutting Ichigo's sword down to just a stump and severely wounding him. Renji is later seen checking on Rukia at her cell, trying to cheer her up by saying that Byakuya wouldn't let her be executed. Despite this, Rukia was aware that she would be executed, knowing that her brother held the laws of the Soul Society above all else.
After Ichigo's group invades the Soul Society to rescue Rukia, Renji goes out to fight him alone, blaming Ichigo for Rukia's troubles. Renji, not operating under a power limit as he was in the human world, does well at first, almost knocking out Ichigo in his first attack. Even after Ichigo figures out that Renji can only perform three consecutive attacks with Zabimaru, Renji easily outmaneuvers him when he attempts to use this to his advantage. Ichigo barely dodges Renji's finishing blow, and begins to pour his reiatsu into Zangetsu. Completely shocked at such refined reiatsu in comparison to their first battle, Renji is finally hit by a direct unnamed Getsuga Tenshō which defeats him and breaks Zabimaru. Before losing consciousness, Renji manages to walk towards Ichigo and explain the reason why he would not save Rukia himself, lamenting "the stray dog" in him. Realizing how powerful Ichigo is, he shamelessly begs Ichigo to save Rukia for him.After being healed, Byakuya has Renji imprisoned, claiming that he had no excuse for losing if he was so eager to fight alone. In his cell, Renji has a conversation with his Zanpakutō's spirit, Zabimaru. While Zabimaru wants a rematch with Zangetsu, Renji insists that they are no longer enemies. He then breaks out of confinement and finds his way to Ichigo, who was in an underground training area with Yoruichi Shihōin, attempting to learn the Bankai of his Zanpakutō. Renji is fairly close to learning it as well, and walks off to a separate part of the training area to complete his training, alongside a materialized Zabimaru. While Ichigo continues to train, Renji manages to achieve Bankai. He attempts to save Rukia on his own, only to be intercepted by Byakuya. Renji attempts to use his Bankai to defeat Byakuya, but both his inexperience and their difference in power leads to his defeat. Renji attempts to charge against Byakuya one last time, but only succeeds in breaking his own Zanpakutō against Byakuya's immense spiritual power. Byakuya leaves a dying Renji with his shawl and acknowledges that Renji's "fang" had finally reached him.
After being healed again, Renji makes another rescue attempt, this time finding Ichigo at the execution grounds with Rukia in tow. From the high perch of the execution stand, Ichigo tosses Rukia to Renji and orders him to defend her with his life. Renji willingly obliges and escapes from the execution grounds with Rukia in his arms. He barely makes it down the winding steps of the mountain they're on before being stopped by Kaname Tōsen, who teleports the three of them back to where they started. Sōsuke Aizen, having also teleported there, insists that Renji leave Rukia. Unwilling to do so, he attacks Aizen with Ichigo Kurosaki, though the latter had not entirely recovered from his encounter with Byakuya. Despite their combined efforts, both are easily defeated. After Aizen's escape, Renji waits in the hospital with Byakuya, who was injured while saving Rukia from Gin Ichimaru. When Byakuya asks why he is there, Renji responds that Byakuya is his captain and that if he weren't alive, Renji would have no one to challenge. Their conversation is interrupted by Ichigo, who was looking all over the Soul Society for Rukia. Renji is then seen at the gathering where Ichigo and his group returned to the human world.
In the anime, after the events at the Soul Society, Renji is assigned to the human world in Rukia's place. While he does not mention exactly why, he is angered at Ichigo's suggestion that he has been demoted from lieutenant. He claims that Ichigo's inability to hide his huge spiritual power attracts Hollows, so he's there to lend a hand. During his visit to the human world, Renji stays at the Urahara Shop where they give him the nickname of nihongo (freeloader) and constantly deny him second helpings of food by playing on his guilt. When Ichigo starts to feel down about his early defeat by one of the Bount, Renji and Ganju Shiba, provoke and attack him, forcing him to realize his strength again. After they Bount fully reveal themselves, Renji joins Ichigo's friends in confronting them at Kariya's mansion, where Jin Kariya sacrifices Yoshino Sōma to create the bitto. While patrolling the city, Renji finds a child being attacked by the bitto and defends him. The bitto eventually withdraw on orders, but Renji is left seriously injured and the child is almost completely drained of his soul. Renji is healed by Hanatarō Yamada, but the child is left struggling to stay alive. A short piece at the end of episode 92 reveals that Hanatarō successfully healed the child.Meanwhile, Izuru Kira, Shūhei Hisagi, Rangiku Matsumoto, and Yumichika Ayasegawa are assigned by Tōshirō Hitsugaya to defeat the Bounts in the human world. The Shinigami find the hideout of the Bount and enter, but are all disabled by Ugaki's doll, Gesell. Renji, Ichigo, and his friends enter the cave later on and are also attacked by Gesell. Most of the group is left to tend to their injuries while Renji and Ichigo continue on, finding the other injured Shinigami along the way. After Gesell almost kills Yumichika Ayasegawa, Renji remembers the fighting spirit he had when he was in the 11th Division and fights Gesell one-on-one with his Bankai. Yumichika keeps Ichigo from interfering, explaining that anyone who's been in the 11th Division believes their fights should be one-on-one, and that helping would be considered dishonorable. Renji manages to wound Gesell, driving it insane and causing it to kill its owner.]
During the brief discussion period between Ichigo and the Shinigami after the Bounts enter Soul Society, an injured Renji (needing Yumichika's help to walk) tells the group he will also be returning to Soul Society. Although he does not enter Soul Society with Ichigo, he is later visited by Tōshirō Hitsugaya, who wants to know if Renji has any helpful information about the Bounts. In Soul Society, Renji, Hitsugaya, and Matsumoto investigate reports of strange activity in a forest in Rukongai. By the time the three of them arrive at the forest, the Bount are gone. Maki Ichinose, on the other hand, is waiting for them, hoping to slow their pursuit and buy time for the Bount. Though initially successful, he is engaged by Kenpachi Zaraki and abandons his plan for the opportunity to kill Kenpachi. After returning to Seireitei, Renji fends off the many Shinigami possessed by the Bount Mabashi's doll, Ritz. After Mabashi is killed, he assists in caring for the wounded. He later helps take Rukia to the execution grounds, where Kariya and Ichigo were fighting.
With the emerging threat of the Arrancar in the human world, General Yamamoto orders Renji, Rukia, Ikkaku, Yumichika, Rangiku, and Hitsugaya to aid Ichigo in the living world, and asks if Ichigo would let them stay at his house. When Ichigo declines, Renji goes to the Urahara shop instead, while Hitsugaya and Rangiku stay in Orihime's home, Ikkaku and Yumichika stay at Keigo Asano's apartment complex, and Rukia stays in Ichigo's house for the duration of their time there. When the sixth Espada leads an unauthorized assault on the Shinigami in the material world, Renji fights the 15th Arrancar,Yylfordt Granz. Even with his Bankai, he is initially no match for him. Things get even worse when Ururu Tsumugiya interferes, injuring Yylfordt and forcing him to release his Zanpakutō. In his released form he impales Ururu with one of his horns and breaks Renji's Zanpakutō effortlessly. The tables are turned however, when Renji's power limit is released, allowing him to defeat Yylfordt with some effort. Renji remarks that if he had been fighting at full power the whole time, Yylfordt would have been more cautious, and might have won. After the battle, Urahara allows him to live at his shop indefinitely. However, Urahara has persisted in avoiding Renji's questions (which is the primary reason as to why Renji decided to go to the shop). During his time there, he helps train Yasutora Sado to increase his ability, because of an agreement Renji made with Urahara: he will do whatever Urahara asks of him for the next three months in exchange for the answers to all of Renji's questions.
When the Arrancar launch a second attack with the purpose of distracting the Shinigami while Orihime Inoue is coerced into working for Aizen, Renji and Chad are left behind at the shop while Urahara goes to aid their allies. When Hitsugaya's team learns that Orihime is with the Arrancar, Renji volunteers for Ichigo's sake to form a team and "force" Orihime back to her senses and bring her back. The request is denied and the team is instead forced to return to the Soul Society under the threat of Byakuya Kuchiki and Kenpachi Zaraki attacking them. Later on however, Byakuya gives both him and Rukia permission to enter Hueco Mundo and fight alongside Ichigo's group. After reaching Aizen's palace and discovering five separate paths, the group prepares to split up. Before they split up, Renji talks to Ichigo about the need to respect his comrades' skills in battle and leads the team in a chant used by the Gotei 13 in the past, vowing to never falter and come out alive together. Afterwards, Renji is mistakenly chased by the Hollow Dondochakka Bilstin, even though they are allies. His appearance and attitude is enough to freak Renji out and convince him to run with the Hollow chasing after him. Both continue for some time after realizing this, arguing that the other should stop first. Eventually, Abarai senses Rukia releasing her Zanpakutō and stops, only to fall into a trap (along with Dondochakka) set by Szayel Aporro Granz, who mocks them and introduces himself. He reveals that the room they're in is designed to suppress Renji's Bankai, which was accomplished by analysing the corpse of his defeated brother, Yylfordt. Renji learns of Rukia's spirit pressure disappearing through Szayel. When Szayel mentions that the Shinigami was called "Kuchiki", Renji, using his Shikai, immediately attacks Szayel. Despite Szayel saying that Renji would not be able to injure him with just his Shikai, Renji manages to do so. Regardless, Renji cannot manage to duplicate the feat, and is saved by Uryū, who quickly ends up in the same situation. The two join forces to deal with Szayel's minions. In order to give Uryū an opening, Renji uses Zabimaru to tie himself and Szayel together, and then uses a Kidō spell which injures them both. Szayel retreats, falling into Uryū's trap, a massive gintō-triggered explosion. Szayel survives the explosion, albeit with near fatal injuries, and heals himself completely by eating Lumina. He then departs to replace his ruined outfit and formulate a new plan. Renji and Uryū try to find a way out of Las Noches because their main target was to retrieve Orihime, not fight an Espada. They should also head out to help Rukia and Chad. However, Szayel manipulates the corridors to make them travel back into the same room. Szayel appears behind them, and releases his Zanpakutō. As soon as the liquid from Szayel's release makes contact with Renji and Uryū, multiple clones of them appear. Szayel then informs them that the device used to restrict their spirit energy has been deactivated, and that they can now fight against their clones at full power. After some time Renji activates his Bankai, causing all of his clones to activate their own. In doing so they destroy the room they are in and a now irritated Szayel disperses all of the clones of Renji and Uryū, saying that he will show them the "true power" of his Fornicarás. Szayel proceeds to use his Voodoo Doll technique on Uryū, which creates an Uryū doll out of him. Szayel hits the doll and reveals that he has control of all of Uryū's five senses. Despite Renji begging him to stop, Szayel rips the doll apart, and although Uryū didn't lose his legs, Szayel crushes the mini stomach organ inside the doll, critically injuring the Quincy. When Renji attacks, Szayel's Zanpakutō swallows Abarai, and creates a miniature Renji doll. Szayel rips the Renji doll in half and crushes his Achilles tendon, making him unable to walk. Though it seems they will be saved by Dondochakka and Pesche Guatiche's new technique, Szayel has analyzed even their strength as well, and easily deflects it. Szayel's further attempts are interrupted however, by Mayuri Kurotsuchi who fights and subsequently defeats the 8th Espada. Kurotsuchi offers heal the two of their wounds, and chooses to heal Uryū first. Renji is concerned that the Espada will kill his friends, and pleads to Mayuri to heal him first since he needs to rejoin the fight; Mayuri reassures Renji that the only one of his comrades still fighting was Zaraki, who had arrived to help Ichigo. Mayuri warns him that Kenpachi and his opponent will tear him apart if he interferes, before he looks inside of Szayel's lab. He is healed of his wounds afterwards, apparently before Uryū as the latter was late to the battle.