Gen suffers from severe medical depression. She can't take it anymore. She couldn't discern the point of her continued existence. She felt helplessly stuck in the miserable life she was forced to live. So when the Doctor accidentally stumbles upon her during the worst moments of her life, Gen is ecstatic. He takes Gen around space and time just like she had hoped to see the world ever since she was a little girl, and tries to make her final few months the best time of her life.