To make Nanimon join the city, go to the Speedy Region where you fought Metiormon and Nanimon will be there. Talk to him, and he will run away, dropping a key chain. Chase him. He is now at Ogremon's Fortress, where you fought Ogremon. Talk to Nanimon, and he will leave. Go to Leomon's cave. He will be where you found the tablet. He will leave again. Go to Toy Mansion, where you fought WaruMonzeamon. Nanimon is there. Talk to him again. He will leave to go to his final hiding area, the sewer. Go a slightly north from Numemon's screen, and Nanimon will be there. He will run away again, dropping another key chain. Go to Jijimon, and he will say: "Nanimon came, then left. I wonder where he is?" Nanimon joined the city. To raise a Nanimon, scold an Agumon when both his Happiness and Discipline are empty.