Korean and Japanese intelligence agencies are again sharing their deepest secrets about their enemies.

That’s the upshot of Thursday’s summit in Tokyo between Korea’s president, Yoon Suk-yeol, and Japan’s prime minister, Fumio Kishida. The deal represents Mr. Yoon’s reversal of a decision by his left-leaning predecessor, Moon Jae-in, who nullified a pact known in both countries as Gsomia, for General Security of Military Information Agreement.

Pronounced “gee-so-mee-a,” the pact has been a matter of often bitter debate ever since a former South Korean president, Park Geun-hye, agreed to the deal in 2016 — more than a year before her impeachment and jailing in the Candlelight Revolution that led to the election of the Mr. Moon.

Renewal of Gsomia has more than symbolic value. Seoul and Tokyo, allied with Washington but not with one another, are now able to tell each other what they know about whatever moves North Korea chooses to make that might jeopardize the security of both countries. They will also presumably be sharing information about China, North Korea’s ally and benefactor.

In repudiating Mr. Moon’s decision, the conservative Mr. Yoon has edged South Korea closer to a de facto alliance with Japan while attempting to resolve long-running animosity dating from Japanese rule over Korea between 1910 and 1945.

Messrs. Yoon and Kishida shook hands on Gsomia 10 days after Korea and Japan agreed on a deal for compensating Koreans forced to work as de facto slave labor in Japanese factories during World War II. 

“The summit meeting indicates an attempted return to normalcy in diplomatic ties between South Korea and Japan,” according to a paper issued by the Center for Strategic and International Studies in Washington.

“After a severe downturn in bilateral ties in 2019 over historical sensitivities and other issues, “ the paper said, “Yoon and Kishida are seeking to establish a durable foundation for the relationship and to expand avenues for cooperation on a range of issues.” 

The most obvious immediate signs of cooperation are ongoing joint South Korean and American military exercises. The state department has said the exercises, the first in five years, are intensifying in response to North Korean threats, including tests of intercontinental ballistic missiles capable, in theory, of firing nuclear warheads to targets anywhere in North America. 

North Korea greeted the Yoon-Kishida summit by firing yet another intercontinental ballistic missile into waters between the two countries. 

South Korea’s Yonhap News quoted Mr. Yoon as saying that he and Mr. Kishida “agreed that in order to respond to the North’s nuclear and missile threats … cooperation among South Korea, the United States and Japan, and between South Korea and Japan, is extremely important.” The North Korean shots, he said, “are getting more sophisticated by the day.”

The decision on Gsomia is sure to reverberate in South Korea, where the opposition Democratic Party still has a majority in the National Assembly. Foes of Japanese-Korean military ties say the Korea compensation deal, in which about $77,000 is to be provided for 15 victims or their surviving families who had sued for payment, ignores the interests of thousands of others. Nor are the Japanese companies or government being compelled to apologize. 

It was due to outraged disagreement on compensation that Mr. Moon canceled Gsomia after Japan spurned an order by Korea’s supreme court for two huge Japanese companies, Mitsubishi Heavy Industries and Nippon Steel, to pay 15 claims. Japan then blocked exports to South Korea of vital material for memory chips. Japan has rescinded the ban, ending, for now, what had been one of the deepest rifts between the two countries.

The summit marked a milestone in Korean-Japan relations — though the bitterness is sure to go on. “I declared the complete normalization of Gsomia,” Mr. Yoon said. “The two countries should be able to share information on North Korea’s nuclear missile launches and trajectories, and respond to them.”

He did not specify what kind of responses would be considered, but the statement suggested Korea and Japan might eventually cooperate on shooting down North Korean missiles — a step that both countries have mentioned but never attempted.