Name the number of vocalists for  which one ~ is it?
CREATE TABLE "pocket_monsters_diamond_pearl_series" (
  "num" real,
  "japanese_title" text,
  "r_maji" text,
  "japanese_translation" text,
  "vocalist" text,
  "episodes_used" text
);
SELECT COUNT("vocalist") FROM "pocket_monsters_diamond_pearl_series" WHERE "japanese_translation"='Which One ~ Is It?';