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In the last chapter of the manga it was shown that Kaizo and Natori were actually patients of a mental ward and that the whole story shown to the readers were actually a part Kaizo and Natori's imagination. It seems that Saien in reality was the doctor in charge of them and in order to help their recovery she let Kaizo and Natori create a city with model buildings and model people. As the city grew the two started to imagine themselves as a part of the city. At the end they made a full recovery and were allow to leave the ward, they got an apartment and started to live together