At first, Doraemon basically has an appearance just like other robotic cat. However, back at the time when doraemon owned by Sewashi, doraemon ear’s got gnawed off by robotic rat. It’s because Sewashi making the model of doraemon, so he took out robotic rat to carve the model of doraemon’s ear but the rat mistook his word and went to the real doraemon to eat his ear. This event causes him to be in depression and drank a potion called sadness. He cried until his colour blue got washed off and this it causes Doraemon to develop musophobia.
Doraemon FC 