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A huge amount of Christian imagery is built up to depict Sora as Jesus and Master Xehanort as Satan, and the realm of Kingdom Hearts as Heaven.
A central part of Sora's character is that he's always taking on the pains and grief of others to ease their burden, he has Chronic Hero Syndrome. Two particularly symbolic moments are when he sacrifices himself to save Kairi and comes back to life, and when he carries a wounded Riku out of the Realm of Darkness. Meanwhile Master Xehanort is The Corrupter to anyone and everyone he can, and is tied up with Fallen Angel symbolism. His Keyblade armor is bright white and silver with feathers and his Keyblade Glider is a set of wings that attached to his back, but he cast his armor and glider away when he began using the powers of darkness and felt he didn't need them anymore.
The Kingdom Key and Kingdom Key D which seal the door to Kingdom Hearts appear as a silver key with a gold handle and a gold key with a silver handle — the Keys of Heaven. The χ-blade appears with two crossed Kingdom Keys in its design, a common depiction of the Keys, and likewise can open the door to Kingdom Hearts. Furthermore, an alternate reading of "χ-blade" could be "Christ-Blade".
As a flip on the Jesus symbolism being applied to Sora, Organization XIII is lead by Xemnas as a Dark Messiah to Nobodies, and Roxas, the thirteenth member, betrays them.
Also a lot of Taoist symbolism, that nothing can exist without its opposite to give it proper meaning, commonly seen in the yin yang symbol. Seen in the balance of light and darkness and the belief that Dark Is Not Evil, its just misused, and the existences of the Nobodies and Heartless. Furthermore, the three realms of Light, Darkness and Nothingness, tie into the "third" element of yin and yang, wuji, nothingness, limitless.