Soak crawfish tail meat in sake for at least 15 minutes.
Mix tempura flour and Creole seasoning well in a large mixing bowl.
To make remoulade, whisk all ingredients, except scallion, in a medium bowl. Keep refrigerated.
When oil is ready for frying, drain crawfish. Working in small batches, pick up a few tail meat pieces at a time and coat well with tempura mix. Fry them for 1-2 minutes, depending on size until they float to the surface and internal temperature reads 165 degrees F. Place on paper towel.
Serve crispy crawfish with remoulade, garnished with sliced scallion.