Prime Minister Narendra Modi and his Japanese counterpart Sanae Takaichi struck a warm personal chord while unveiling an ambitious roadmap to deepen India-Japan ties during the 16th Annual Summit in New Delhi. Calling the India-Japan relationship a "partnership of strategic convergence and trust for shared growth, prosperity and resilience," the two leaders said the phrase reflected "the substance and progress of our partnership." The camaraderie between the two leaders was also on full display when Takaichi revealed that Modi had called her his "beautiful younger sister," adding that they had agreed to take the relationship forward "as brother and sister."Prime Minister Narendra Modi greets Japanese Prime Minister Sanae Takaichi during the India-Japan Joint Economic Forum, in New Delhi. (DPR PMO)Beyond the light-hearted exchange, the summit underscored what both sides described as a "mutually complementary relationship" in an increasingly uncertain global environment, with cooperation spanning defence, economic security, technology, energy and regional stability.Here are the five biggest takeaways:1. Strategic partnership gets a fresh pushThe two leaders reaffirmed their commitment to strengthening the India-Japan Special Strategic and Global Partnership, identifying defence and security, economic resilience, technology and innovation, and people-to-people exchanges as the three key pillars for future cooperation. They described India and Japan as "natural and indispensable partners" amid growing geopolitical uncertainty.Also Read: AI, defence, healthcare: What was discussed in Modi's meet with Japan PM Sanae Takaichi2. Defence cooperation moves into higher gearIndia and Japan agreed to deepen military cooperation through more maritime exercises, greater maritime domain awareness, defence equipment collaboration and technology transfer. The two sides also announced that the next 2+2 Ministerial Meeting will be held in Tokyo later this year and welcomed progress on the UNICORN defence communications project.3. Economic security and technology take centre stageRecognising vulnerabilities in global supply chains, the two countries adopted a Joint Declaration on Economic Security Cooperation focused on semiconductors, critical minerals, clean energy, pharmaceuticals and information technology. The leaders also launched a new AI cooperation framework aimed at promoting trusted digital infrastructure and responsible artificial intelligence.4. Energy and infrastructure remain major focus areasThe summit saw renewed emphasis on clean energy, including biogas, hydrogen and ammonia projects, alongside cooperation on strategic petroleum reserves. Japan also reiterated its commitment to India's flagship Mumbai-Ahmedabad High-Speed Rail project and expressed willingness to support future high-speed rail corridors across the country.Also Read: Chips over subs: Why Sanae Takaichi's India visit is about economics first5. Shared concerns over regional securityThe two leaders voiced concern over developments in the South China Sea, North Korea's missile programme and terrorism, including cross-border terrorism from Pakistan. They reaffirmed support for a free and open Indo-Pacific, stronger Quad cooperation and reforms of the UN Security Council while also backing each other's bid for permanent membership.The summit concluded with Takaichi inviting Modi to Japan next year for the 17th Annual Summit, signalling that the "brother-sister" rapport will be accompanied by a broader strategic partnership that both sides hope will shape the Indo-Pacific's future