Bring mirin to the boil in a small pot. Remove from heat and add the soy, vinegar, lime juice and dashi. Set aside.
Remove oysters from the shell. Wash the shells and place them on top of ice or just a plate.
Bring some water to the boil in a medium-sized pot and reduce the heat to simmer. Add oysters and poach them for 30 seconds. Remove the oysters from the hot water and put them back in each shell. Drizzle with ponzu sauce (don't use too much) and add tobiko.
Garnish with edible flowers and micro herbs if you have them.