The International Tribunal for the Law of the Sea (ITLOS) was established by the UN Convention on the Law of the Sea and is composed of 21 judges. The first Japanese judge, Professor Yamamoto Soji, served one term of nine years, after which the author served two terms of 18 years. The majority of judges strive to find the best solution for the cases that are referred to them, so the direction of the judgment is determined through repeated discussions among the judges. ITLOS has been highly regarded around the world in the 30 years since its establishment, and it has begun to accept large cases such as boundary delimitation cases, and its precedents are contributing to the development of the Law of the Sea.

ITLOS was established by the UN Convention on the Law of the Sea (UNCLOS), which was adopted in 1982, as a specialized court for resolving maritime disputes between states, and began operations in 1996. ITLOS is composed of 21 judges chosen through international elections from among the world's experts on the Law of the Sea. From Japan, Professor Yamamoto Soji, an authority on the law of the sea, was elected in the first election and served a 9-year term. In 2004, the year before his term was to expire, the Ministry of Foreign Affairs asked the author to become the next judge. Professor Yamamoto also told him, "I want to retire after one term. You should take over." The author initially decided it was time to relax and declined the request, but after strong persuasion from the Ministry of Foreign Affairs and Professor Yamamoto, he reluctantly ran for the position and was elected with a high score. About five years into his first term, ITLOS needed to elect a new president through mutual selection. Although the author had no intention of becoming president, he was unanimously elected through his colleagues' recommendation.
The president's term is three years, during which one must reside permanently in Hamburg, Germany. In addition to serving as the presiding judge for cases, he also chairs the drafting committee responsible for creating draft judgments. When a case is submitted to ITLOS as a full court, the drafting committee typically consists of five judges, including the chair, with each member drafting portions of the initial draft. Despite receiving general direction from the full court, drafting the first draft from scratch is an enormous task. Draft judgments are created through up to three drafts before voting. The president also manages the court's administrative and financial affairs and represents the court at international conferences such as the UN General Assembly, making it an extremely demanding role. He was persuaded by the Ministry of Foreign Affairs and his predecessor, Judge Yamamoto, to take the position of judge. After being reelected, the author ultimately served two terms totaling 18 years, retiring in May 2024.

The number of 21 judges in ITLOS is significantly larger than the 15 in the International Court of Justice (ICJ), which has existed for a long time. This is primarily because developing countries argued that the composition of ITLOS judges should better represent each region of the world. When the author first assumed his post at ITLOS, he was very anxious about whether a majority opinion could be reached among 21 judges for each case. In terms of actual contentious cases, first each of the parties to the disputes concerned typically submits two written statements, followed by oral arguments in court. In the full court, the 21 judges will discuss and strive to find a judgment’s direction after hearing the arguments of the parties concerned. Indeed, at the beginning of such deliberations, there are countless arguments and it seems unresolvable at first glance, but as discussions continue, they slowly head towards finding a solution. These 21 judges come from 21 different countries, and are legal professionals working with different languages, cultures, and even legal systems as backgrounds. Despite these differences, he felt they were able to reach a resolution because the majority of the judges strive to find the best possible solution for the case. For smaller five-judge chambers, reaching consensus is easier. Through 18 years of experience, the author learned that a kind of "collective wisdom" emerges from discussions. He also gained much knowledge through discussions with outstanding legal professionals from around the world, including judges from developing countries.

ITLOS has received 33 cases and issued judgments or decisions on 27 of them. In the first decade after ITLOS was established, most cases involved urgent procedural matters like prompt release of foreign fishing vessels captured in the exclusive economic zones (EEZ) of coastal states and provisional measures protecting the rights of the parties to a dispute. However, as ITLOS's global recognition grew, it began to be entrusted with major cases such as regarding damage compensation for merchant ship seizures, the delimitation of territorial waters, EEZs and the continental shelf,and advisory opinions clarifying the interpretation of UNCLOS. Japan has been involved in several cases, appearing before ITLOS as both defendant and plaintiff, having been filed against by New Zealand and Australia in the "Southern Bluefin Tuna" case and filing against Russia in the "Hoshinmaru" and "Tomimaru" cases.
In international law, including the law of the sea, jurisprudence in international courts plays a crucial role in forming and clarifying rules, with the ICJ being a prime example. ITLOS has also contributed to the formation of such case law through nearly 30 years of activity. The main examples of ITLOS's jurisprudence contributing to the development of the law of the sea include the following. In today's marine transport, vessel owners, crew members, cargo owners, and others are multinational. In cases where a ship is seized by a foreign country, it becomes practically impossible for the individual parties’ home countries to protect their interests through diplomatic protection. Therefore, ITLOS established a principle where the flag state (the country where the ship is registered) protects the interests of these multinational stakeholders as a whole, treating the vessel as a unit including crew members, cargo, and other components. Regarding the system of early release of fishing vessels detained in the EEZ upon payment of a "reasonable bond," ITLOS specifically clarified the meaning of "reasonable." Additionally, ITLOS became the first international court to conduct the delimitation of the continental shelf beyond 200 nautical miles in the dispute between Bangladesh and Myanmar over the continental shelf in the Bay of Bengal. ITLOS also ruled that coastal states have the right to regulate when foreign tankers and other vessels provide bunkering (underway replenishment), a business that developed after the adoption of UNCLOS, to foreign fishing vessels within the EEZ. Furthermore, ITLOS has clarified unclear provisions of UNCLOS through three advisory opinions concerning deep seabed activities, illegal, unreported, and unregulated (IUU) fishing, and climate change.

*Served as Judge of ITLOS from 2005 to 2024 (President of said Court from 2011 to 2024)