Disputes with RUSSIA:
Former Soviet Union and now Russia owns all these islands. Some of these islands still retained their Japanese name. Many of these islands are still inhabited by Japanese speakers who practice Japanese customs. The closest islands are so close to Japan that you can see them with your naked eyes from japanese land.
This is the oldest map in the world of this region (Sakhalin or Karafuto) (written in Japanese):

My grandfather was born on Karafuto but now he cannot return to his birthland.
"The Kuril Islands (Russian: Кури́льские острова́), also known as Kurile Islands, stretch northeast from Hokkaido, Japan, to Kamchatka, separating the Sea of Okhotsk from the North Pacific Ocean. They are part of Russia's Sakhalin Oblast.
The islands are known in Japanese as the 千島 - Chishima (the thousand islands) or クリル列島 - Kuriru rettō (Kuril Archipelago). The name originates from the autonym of the aboriginal Ainu: "kur", meaning man.
The Kuril Islands were inhabited by the Ainu from time immemorial until they were expelled from the northernmost by the Russians in the 18th century. Japan inherited them in 1875 (Treaty of Saint Petersburg) in exchange for ceding Sakhalin to Russia. Russia reclaimed them after the WWII (Treaty of San Francisco), but Japan maintains a claim to the four southernmost islands, called Northern Territories in Japan (see Kuril Island conflict).
The islands are renowned for their fogginess but are rich in seaweed and marine life, such as fish and otters. The northernmost, Atlasov Island (Oyakoba to the Japanese), is an almost perfect volcanic cone rising sheer out of the sea and has led to many Japanese eulogies in haiku, wood-block prints, etc., extolling its beauty, much as they do the more well-known Fuji."
sourceDisputes with CHINA

"Accordingly, the Senkaku Islands are not included in the territory which Japan renounced under Article II of the San Francisco Peace Treaty. The Senkaku Islands have been placed under the administration of the United States of America as part of the Nansei Shoto Islands, in accordance with Article III of the said treaty, and are included in the area, the administrative rights over which were reverted to Japan in accordance with the Agreement Between Japan and the United States of America Concerning the Ryukyu Islands and the Daito Islands signed on 17 June 1971. The facts outlined herein clearly indicate the status of the Senkaku Islands being part of the territory of Japan."
sourceDisputes with KOREA
"In 1904, a resident of the Oki Islands, Yozaburo Nakai, requested the government to incorporate Takeshima as a territory and lease it out for the purpose of sea lion hunting. In response to this, the government officially named the islands Takeshima during a cabinet meeting on January 28th 1905, and designated it the property of the Oki Islands in Shimane Prefecture. Based on this, the Governor of Shimane Prefecture announced the details in the 40th Shimane Prefectural Report on February 22nd of the same year.
The islands were also entered in the State Land Register for Oki-no-kuni, District 4 in the same year. All requirements under international law, including the approval of sea lion hunting in accordance with fisheries supervision rules, the construction of a large temporary signpost for passing ships, inspection by the Governor, and site surveys by officials from Shimane Prefecture, Division 3, were carried out to full satisfaction.
In addition, the fishing dwellings and other buildings put up by Yozaburo Nakai and related parties were used throughout the years, and under effective Japanese control until the end of World War II.
In accordance with international law, Takeshima clearly belongs to Japan."
source"Upon Japan's defeat and occupation by the Allies, SCAP Instruction #677 of January 29, 1946 excluded the islands from Japan's administrative authority. However, the instruction specifically stated that it was not an 'ultimate determination' of the islands' fate, and all other islands listed in the document were eventually returned to Japan. The 1952 Treaty of San Francisco, which settled the sovereignty of most other disputed islands, did not mention the islands.
On April 20, 1953, South Korean volunteer coast guards set up camp on the island. On June 27, 1953, two Japanese coast guard vessels landed on the East Islet, drove off the Korean guards and set up a territorial marker, but did not attempt permanent occupation. The Koreans soon returned and several armed skirmishes followed, leading to the sinking of a Japanese ship by Korean mortar fire on April 21, 1954. Japan protested and suggested arbitration at the International Court of Justice, but the offer was rejected by South Korea. After the incident, South Korea built a lighthouse and helicopter landing pad on the islet, which it has occupied ever since."
source