In many ways, Yogendra Puranik is an immigrant success story. Puranik, 45, joined the initial wave of Indian tech workers who went to Japan in the early 2000s. He became a Japanese citizen and in 2019 won elected office in Tokyo, a first for anyone from India. This year, he was hired as the principal of a public school. Now, though, as Japanese companies scramble to lure more highly educated Indians like Puranik to fill a yawning shortage of IT engineers, he is under no illusion about the challenges that Japan, and those it attracts, will face. Recruiters call it...