The Asian city designated by Spain as a royal and loyal city was Manila.
Spanish forces led by Miguel López de Legazpi established Manila as a colonial city in 1571, choosing its strategic position on the island of Luzon near Manila Bay. Its excellent harbor connected the Philippines to China, Southeast Asia, Mexico, and Spain, making it the capital of the Spanish East Indies.
In 1574, King Philip II confirmed Manila’s title “Insigne y Siempre Leal Ciudad,” commonly translated as “Distinguished and Ever Loyal City.” The honor recognized the city’s loyalty and the hardships endured by its inhabitants during Spain’s conquest and consolidation of the Philippines.
Manila later became the Asian endpoint of the Manila–Acapulco Galleon Trade, which linked the Philippines and Mexico across the Pacific from 1565 to 1815. A frequent mix-up is Intramuros, the walled historic core of Manila; Intramuros is part of the city, not a separate answer.