The central twist of "A Whisker Away" is the true nature of the Mask Seller's bargain. Miyo initially believes she can switch between being a human and a cat at will. However, after a particularly painful rejection from Hinode, she rashly decides she wants to be a cat forever. At this moment, her human face literally falls off in the form of a mask, which the Mask Seller snatches. He reveals that his goal is to trade human lives for cat lives, taking the remaining lifespan of the human for himself to extend his own life. Miyo is now trapped as a cat and begins to lose her human consciousness.
The plot is further complicated when Kinako, the stepmother's aging cat, takes Miyo's human mask and transforms into Miyo to experience human life and be closer to her owner, Kaoru. This 'fake Miyo' acts out of character, which makes Hinode suspicious. Kinako, seeing how sad Kaoru is without her, has a change of heart and decides to help Miyo. She reveals the secret to Hinode, leading him to the hidden Cat Island to save Miyo. On the island, they confront the Mask Seller and are aided by other resentful humans he has trapped as cats. They successfully retrieve Miyo's face, and both she and Hinode confess their true feelings for each other. The ending reveals that true connection was possible only after Miyo chose to embrace her human life, with all its imperfections, and both characters learned to communicate honestly.