The swordsman Yakage acquired Kageba as part of his dream to create his magnum opus: the Lightning Eagle Sword. He intended to study Kageba to advance his research into the arts of swordcrafting, but Hishima of the Shima Brothers appeared and threatened to kill Yakage's daughter Minagi (who was unconscious in a healing tank nearby) unless he surrendered Kageba to him. As Yakage lifted Kageba in defense of someone he cared for, Kageba generated a powerful aura around him, but when Yakage handed the blade over to Hishima, the aura moved to him, as if Hishima was also trying to protect someone he cared about by stealing Kageba.
Years after Yakage's death, Minagi discovered his journal and read about the theft of Kageba from her father's perspective. Minagi began to blame herself for the theft, so one month later, in 150,081 CMT, she tracked down her mother and sister aboard the Bebop II and told them that she wanted to find and reclaim Kageba.