It had been two years since the end of the winter war. Two years since Kurosaki Ichigo had defeated Aizen not by using Mugetsu, but by using his training in the Dangai Precipice to convert all his spiritual energy into physical strength and using it to literally take Aizen's head, his shield unable to withstand the young shinigami's full-power blow. Two years since Gin was critically injured from an attempted assassination on Aizen and the traitor Tosen preceded his master to the grave. Gin has fully recovered since and after a trial where it was revealed he had been working as a double-agent AGAINST Aizen for nearly a century in an attempt to find a weakness and bring him down, was given a full pardon and allowed to return to his Captain's duties.
Hisagi Shuuhei had been promoted to the level of Captain and chosen a new Lieutenant for the 9th squad, however Squad 5 had only an acting-Captain. Lieutenant Hinamori Momo, who's mental state had been iffy at best during the war, had made a complete turnaround once Ichigo had taken an interest in her plight. Turns out he was the best man for the job of pulling her out of her funk because he understood her pain - the feeling of loss was overpowering the feeling of betrayal. As Ichigo had put things, the Aizen she had known, the Captain she had loved, died the day he showed his true colors. Even if the person never truly existed, he existed in Momo's heart, and that's all that matters. The other Shinigami were shocked at how similar Kurosaki and Hinamori dealt with the loss of their most important people: Kurosaki was only able to pull himself out of his despair because he had younger sisters who needed him. Momo had no such person, so Kurosaki helped her out, opening up to her fully as a result. Momo now knew more about the substitute than even his own nakama, and gained strength from the deep show of trust. A leap of faith taken to save HER. She adamantly refused any captain nominations to her squad, saying she needed someone she knew she could trust. Which was why, now two years since Aizen's defeat, a recently-graduated Kurosaki Ichigo was saying his farewells to lead his new squad. His family and his nakama knew the 5th Squad needed him more than they did, and while sad to see him go, knew it was for the best.