S is for Sandcastle:

"Wet sand builds better," Riku sneers at Sora's attempts to dig higher up the tideline.

Sora grins and says, "We'll see whose is standing last," while Kairi gathers thalassa shells from tidepools.

Riku's is bigger and more elaborate, but the tide comes in over it before Kairi's done exclaiming over Sora's.

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I still can't give him a happy ending, dammit.