What's the symbolism behind the backgrounds shown in the opening sequence? In the opening sequence of Samurai Champloo, when Mugen and Jin are shown, the background is composed of pictures of roosters and aquatic animals, respectively.
Mugen has roosters for background:

Jin has fishes and octopus in his background picture:

What is the symbolism behind such background depiction?
Roosters are a traditional symbol of Shintoism, associated with the sun goddess Amaterasu. Shinto is a philosophy indigenous to Japan, and therefore thematically related to loyalty &amp; nationality, like Mugen.

Jin's main fish is colored like a koi, the Japanese word for "carp". Koi are obviously symbols of Japanese culture, associated with love &amp; friendship. Aquatic life is from the ocean, the realm of the storm god Susanoo, Amaterasu's sibling &amp; counterpart.

Check out the story of Amaterasu &amp; Susanoo, as it has obvious parallels to Mugen &amp; Jin's relationship. Interestingly enough, they have a third sibling, Tsukuyomi, the god of the moon, who acted as a foil, kind of like Fuu. And Tsukuyomi's falling out with Amaterasu resulted from a conflict with the goddess of food... "Her stomach is like a cosmos unto itself!"