What present-day country lies to the east of Japan,
across the Pacific Ocean

East Sea or Sea of Japan (same name but different versions)

Explanation:

"Sea of Japan, Japanese Nihon-kai, Russian Yaponskoye More, also called East Sea, Korean Tonghae or Donghae, marginal sea of the western Pacific Ocean. It is bounded by Japan and Sakhalin Island to the east and by Russia and Korea on the Asian mainland to the west. Its area is 377,600 square miles (978,000 square km)" (Britannica).

i think that the answer is polishing peanuts