This ship bigger than its counterpart in the Japanese navy, and in fact is the largest of its kind in Asia. But most provocative of all to Japan is the ship's name: the LPX Dokdo. "Dokdo" is the Korean name for islets in the Sea of Japan that are clamed by both South Korea and Japan. (The islets are known in English as Liancourt Rocks and in Japanese as Takeshima [竹島].)
This was simply the most recent (but a very in-your-face) resurfacing of a dispute that goes back centuries. The dispute has less to do with the islands themselves, which are essentially uninhabitable, than with the oil and natural-gas desposits under the sea floor around the islands.