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The female lead seemed to be from some organization. Because her brother had sacrificed himself in the previous mission, she promised to finish the last one and then quit. In all the stories, the male protagonist was alone. In the beginning, he was the lord of some city. Later, the female protagonist turned into a little girl and played a system game with the male protagonist. There was also a time when the female protagonist turned into a zombie in the apocalypse... The male protagonist was the female protagonist's patient, so the female protagonist went to various planes to heal him. However, the female protagonist was actually the patient in the real world. The female protagonist had traveled through these worlds before, and it was the male protagonist who helped her wake up. The female protagonist got into a car accident in the real world, and that was all she remembered.