Day & Night follows two characters, Day and Night. Inside Day is a day scene with a sun in the center, and inside Night is a night scene with a moon in the center. Whatever goes on inside of Day or Night expresses normal events that typically occur within a day or night, respectively, and these events often correspond with actions or emotions that Day or Night express or receive. For example, when Day is happy he will have a rainbow inside him, and when Night is happy he will have fireworks inside him.
Day and Night meet and at first, they are uneasy about each other. They are dismissive of each other because each perceives the other as being different, and their prejudices result in a physical altercation between the two. However, as the characters discover the many fascinating events that occur in each other, they learn to appreciate them and learn to like one another.
At the end of the film, the Sun descends in Day and rises in Night, so that when the Sun is at the same height above the horizon in each, both characters appear to be identical. As the Sun continues its course, Day becomes Night, and Night becomes Day. The meaning of this film is that day and night are one. Day cannot exist without night, nor night without day.