Yamaguchi Masashi studied the Vietnamese Language at university. Since joining the International News Division in 2014, he has focused on Southeast Asian politics, economics, and social issues. He has reported on the democratization of Myanmar, the South China Sea Arbitration between the Philippines and China, and other events.

From 2018, he has been serving as the Manila bureau chief. He is now focusing on social issues such as poverty in the Philippines and diplomatic relations between the Philippines and China, including issues surrounding the South China Sea.