This means nothing to Japan and this should only be interpreted as India developing.
It now has the largest population so, everything else being equal, it should ultimately be the largest or second largest economy on the planet. This does not imply that others are doing poorly.
Japan's economy has been pretty stagnant since before I was born. So scared perhaps, but shocked is a ridiculous word to describe a clear trend that started nearly 30 years ago.
JP's 2023 nominal/dollar GDP @4.2T is like 65% of previous peak @6.2T due to USD strenghening. USD strengthened another 15% in 2024 so JP nominal GDP probably 55% of peak now. Per capita GDP dropped from 50k usd to 34k USD. Apart from FX drama that makes JP buying imports/going abroad difficult (while dealing with tourists), also general sign that JP's effort to improve business enviroment last couple decades have been failing. They can try to strenghten yen / but then lose exports to bother producers.
It now has the largest population so, everything else being equal, it should ultimately be the largest or second largest economy on the planet. This does not imply that others are doing poorly.