If using salt-preserved cherry blossoms: soak in cold water for 20 to 30 minutes, switching out the water at least once halfway through. Finish with a final cold rinse and set aside.
In a medium saucepan, combine water and sugar. Cook over medium heat until it reaches a gentle boil.
Reduce heat to low. Add the hibiscus petals (or freeze-dried raspberries) and cherry blossoms.
Simmer for 5 minutes, then remove from heat.
Remove the hibiscus petals. Let the syrup cool to room temperature with the blossoms still in it.
Strain through a cheesecloth to remove the cherry blossoms and any fine particles. Transfer to a clean glass mason jar. Refrigerate for up to a week, or freeze in portions.