All the staff members of Japan Expo have been instructed to bring back any lost item to the Info Point during the festival. If you don't know it or if your object has not been dropped off yet, you can write to the following e-mail
Lost and found items are kept on our premises. Send us a precise description, and we will check if the object is in our possession! We will get back to you if it is.
And don't give up hope! Great stories often happen at Japan Expo!