In this photo from a vintage publication Maj General Nishihara Issaku (on the left) is ready to take off from Haneda airport with three other officers on June 26, 1940 to inspect whether the colonial authorities of French Indochina are enforcing the blockade of weapons towards Chiang Kai-shek that came into effect after the strong protests of the Japanese.
Wikipedia has good entry about Nishihara and his involvement in the negotiations with the French.
"In early 1940, troops of the Imperial Japanese Army (IJA) moved to seize southern Guangxi and Longzhou County, where the eastern branch of the Kunming–Hai Phong Railway reached the border at the Friendship Pass in Pingxiang. They also tried to move west to cut the rail line to Kunming. The railway from Indochina was the Chinese government's last secure overland link to the outside world.
On 19 June, Japan took advantage of the defeat of France and the impending armistice to present the Governor-General of Indochina, Georges Catroux, with a request, in fact an ultimatum, demanding the closure of all supply routes to China and the admission of a 40-man Japanese inspection team under General Issaku Nishihara. The Americans became aware of the true nature of the Japanese "request" through intelligence intercepts, since the Japanese had informed their German allies. Catroux initially responded by warning the Japanese that their unspecified "other measures" would be a breach of sovereignty. He was reluctant to acquiesce to the Japanese, but with his intelligence reporting that Japanese army and navy units were moving into threatening positions, the French government was not prepared for a protracted defense of the colony. Therefore, Catroux complied with the Japanese ultimatum on 20 June. Before the end of June the last train carrying munitions crossed the border bound for Kunming. Following this humiliation, Catroux was immediately replaced as governor-general by Admiral Jean Decoux. He did not return to France, however, but to London.
On 22 June, while Catroux was still in his post, the Japanese issued a second demand: naval basing rights at Guangzhouwan and the total closure of the Chinese border by 7 July. Issaku Nishihara, who was to lead the "inspection team", the true purpose of which was unknown, even to the Japanese, arrived in Hanoi on 29 June. On 3 July, he issued a third demand: air bases and the right to transit combat troops through Indochina. These new demands were referred to the government in France.
The incoming governor, Decoux, who arrived in Indochina in July, urged the government to reject the demands. Although he believed that Indochina could not defend itself against a Japanese invasion, Decoux believed it was strong enough to dissuade Japan from invading. At Vichy, General Jules-Antoine Bührer, chief of the Colonial General Staff, counselled resistance. The still neutral United States had already been contracted to provide aircraft, and there were 4,000 Tirailleurs sénégalais in Djibouti that could be shipped to Indochina in case of need. In Indochina, Decoux had under his command 32,000 regulars, plus 17,000 auxiliaries, although they were all ill-equipped.
On 30 August 1940, the Japanese foreign minister, Yōsuke Matsuoka, approved a draft proposal submitted by his French colleague, Paul Baudouin, whereby Japanese forces could be stationed in and transit through Indochina only for the duration of the Sino-Japanese War. Both governments then "instructed their military representatives in Indochina to work out the details [although] they would have been better advised to stick to Tokyo–Vichy channels a bit longer". Negotiations between the supreme commander of Indochinese troops, Maurice Martin, and General Nishihara began at Hanoi on 3 September.
During negotiations, the government in France asked the German government to intervene to moderate its ally's demands. The Germans did nothing. Decoux and Martin, acting on their own, looked for help from the American and British consuls in Hanoi, and even consulted with the Chinese government on joint defence against a Japanese attack on Indochina.
On 6 September, an infantry battalion of the Japanese Twenty-Second Army based in Nanning violated the Indochinese border near the French fort at Đồng Đăng. The Twenty-Second Army was a part of the Japanese Southern China Area Army, whose officers, remembering the Mukden incident of 1931, were trying to force their superiors to adopt a more aggressive policy. Following the Đồng Đăng incident, Decoux cut off negotiations. On 18 September, Nishihara sent him an ultimatum, warning that Japanese troops would enter Indochina regardless of any French agreement at 22:00 (local time) on 22 September. This prompted Decoux to demand a reduction in the number of Japanese troops that would be stationed in Indochina. The Japanese Army General Staff, with the support of the Japanese Southern China Area Army, was demanding 25,000 troops in Indochina. Nishihara, with the support of the Imperial General Headquarters, got that number reduced to 6,000 on 21 September.
Seven and a half hours before the expiration of the Japanese ultimatum on 22 September, Martin and Nishihara signed an agreement authorizing the stationing of 6,000 Japanese troops in Tonkin north of the Red River, the use of four airfields in Tonkin, the right to move up to 25,000 troops through Tonkin to Yunnan and the right to move one division of the Twenty-Second Army through Tonkin via Haiphong for use elsewhere in China. Already on 5 September, the Japanese Southern Army had organized the amphibious Indochina Expeditionary Army under Major-General Takuma Nishimura, it was supported by a flotilla of ships and aircraft, both carrier- and land-based. When the accord was signed, a convoy was waiting off Hainan Island to bring the expeditionary force to Tonkin.