Slice the chicken breast diagonally into bite-sized pieces. Place in a bowl, add sake and salt, and massage. Let sit for 5 minutes, then coat with potato starch.

Boil water in a pot, add the chicken, and cook on low heat for 2–3 minutes until done. Transfer to ice water to cool, then drain.

Cut the mentaiko open and scoop out the contents with a spoon.

Mix mentaiko, mayonnaise, and milk in a bowl to make the mentaiko mayo.