In a bowl or liquid measuring cup, combine the warm water, yuzu marmalade, sugar, and salt. Whisk until the sugar and marmalade syrup are completely dissolved.
Optional: for a fully smooth sorbet, pulse the mixture with an immersion blender for 5 seconds to break up the candied peel. For citrus flecks, leave as-is (the Creami paddle will chop the rind during spinning).
Stir in the pure yuzu juice.
Pour the liquid into a Ninja Creami pint (do not exceed the MAX FILL line). Snap on the lid and freeze on a flat, level surface for 24 hours.
Remove the pint from the freezer, assemble into the outer bowl, lock it into the machine, and press SORBET.
If smooth and glossy, serve immediately. If crumbly or powdery, add 1 tablespoon of water into the center and run a RESPIN.
Notes
Prep time: about 5 minutes; freeze time: 24 hours.