Remove the contents of the mentaiko.

Cut the boiled eggs into bite-sized pieces. Thinly slice the cucumber, sprinkle with a little salt, and let sit for 5 minutes until softened. Rinse and squeeze out excess water.

Boil a pot of water, add a pinch of salt, and cook the macaroni according to package instructions. Drain well.

While the macaroni is still hot, place it in a bowl and mix with vinegar. Let it cool to room temperature.