Synopsis
Fandom WikiNobita receives a phone call from Shizuka who is trying to bake a chocolate cake for him, but she is having trouble with Peeko when her pet bird escaped his cage and flies around in the kitchen. Meanwhile, Doraemon prepares to go on a date with Mii-chan. Nobita asked for Doraemon's help, but the earless robot cat had already left. So Nobita looked into the spare 4D pocket and found a box of and took the one that looks like a chicken. Leaving the box unintended and opened, Mii-chan enters Nobita's room.
At Shizuka's house, Nobita arrives to help her out with Peeko. He eats the chicken-shaped biscuit and transforms into a giant chicken. Communicating with Peeko, he managed to return the little pet bird back into the cage much to Shizuka's relief and thankfulness. While walking back home in his chicken form, Nobita bumps into Doraemon. Curious as to how Nobita got his hands on the Animal Transformation Biscuits, he and Doraemon rushed back home. When Doraemon examined the fallen box of Animal Transformation Biscuits, he thinks that Mii-chan may have one and turned into a frog much to Doraemon's concern. He frantically runs out the house with Nobita following.
Suneo was just walking along with a big heart-shaped chocolate. Then the frog turns into a hippopotamus scaring Suneo and eating his chocolate heart. Doraemon and Nobita find the hippo at the empty lot thinking it is Mii-chan who ate more than one Animal Transformation Biscuit. As Doraemon approached the hippo, it trampled and flattened him into a pancake for a few seconds. Before chasing the hippo, Nobita criticized Suneo for buying a pointlessly expensive gift for someone leaving Suneo bawling like a baby and humiliated. During the chase, the hippo turns into a lion, which frightened everybody within the its vicinity. The lion breaks into Gian's home scaring Gian who was about to have lunch. Then Nobita and Doraemon passed by. At the last traffic stop, the lion turns into a turtle. Relieved, Doraemon is about to pick the turtle up until it bit him in the hand.
Back at home, Doraemon is happy to have Mii-chan back safe and sound. But when the turtle turned into a mouse, Doraemon's joy is replaced with fear as he bounced around Nobita's room. Nobita stated that the mouse could be Mii-chan in rodent form and told Doraemon to visualize Mii-chan not as a mouse. Meanwhile, Shizuka has finished baking a cake and walks over to Nobita's house with the real Mii-chan following her. Back at Nobita's house and outside on the rooftop, Doraemon dates the mouse while trying his best to overcome his fear. He even fed and defended the mouse from the hungry cats.
Shizuka has arrived at Nobita's house and presented him a cake she baked for him to which he happily thanked. When he noticed the real Mii-chan behind Shizuka, he thought she had finished her date with Doraemon until he realizes that Doraemon is dating a real mouse the entire time much to his surprise. While on a hot-air balloon ride, Doraemon has finally conquered his fear of mice while still dating the mouse. However, when Nobita called out to Doraemon, he and Shizuka showed the real Mii-chan is on the ground. Learning the truth caused Doraemon's fear of mice to return permanently as he began acting like an idiot trying to avoid the mouse he was dating much to Nobita's disbelief towards Doraemon's ignorant behavior and saying Doraemon's usual phrase "Oh, brother."