This is a chilled tomato salad. You can make it in advance. It looks quite elegant too, so I recommend it for parties! It's a perfect tomato salad for the summer.
My mother used to make this for me, recreating the salad she had at a restaurant she used to go to a lot.
I don't have any hints really. Just chill it well in the refrigerator before serving. You can make this in advance so it's very convenient, and looks very elegant too.
Enjoy Japanese food around the world.