Doraemon: Nobita and the Steel Troops

When giant robot parts suddenly fell from the sky, Nobita and Doraemon secretly took them into the mirror world to assemble a massive machine they named Zandacross. Realizing it was a dangerous weapon, they kept its existence hidden. Then a mysterious girl named Riruru appeared, demanding Zandacross to aid an invasion-though she herself refused to support the attack on Earth. Now, Doraemon and his friends must work together to stop the advancing robot army, but the key to ending the conflict may lie with Riruru alone.