Ichigo must fight the very mentor who taught him how to use his power. Zangetsu uses Ichigo's own techniques against him, proving that the blade knows the wielder better than the wielder knows himself.

While technically a "filler" episode—meaning it wasn't in the original manga—this story is highly regarded by fans on platforms like Facebook because it provides a rare, deep dive into the complex relationship between a Shinigami and their sword. It highlights the fragility of Ichigo's power and sets the stage for him to eventually reclaim and redefine his connection to Zangetsu. Zengetsu becomes an enemy in bleach - Facebook

With Zangetsu "released" and no longer acting as a seal or guide, Ichigo’s Inner Hollow begins to surge. Without the stabilizing presence of his Zanpakuto, the monstrous side of Ichigo’s power threatens to take full control of his body. Why This Story Matters