He is a friend of Momo Hinamori and Renji Abarai from their days in the Soul Reaper academy, and the three often spend their free time together. Though Kira is loyal to his friends, he often places his duties as a lieutenant above them. He defends his captain, Gin Ichimaru, from a grief-stricken Hinamori, and later calls himself a "monster" for raising his sword against her.He subsequently comes to regret helping Gin to defect from Soul Society, and develops more of a depressed and pessimistic demeanor.