I’m not sure exactly why it’s 49 days, but the Tibetan Book of the Dead describes it pretty vividly. Essentially your Buddha nature spends 49 days in the Bardo *sort of a Buddhist purgatory” seeing different manifestations of the Buddha, which may or may not terrify you depending on what you did or didn’t do while you were alive. If you are scared you run away from them. Eventually, though, I assume on the 49th day, you will be drawn to one of them and that will determine your next life.

And even though Japanese people have become more secular since the end of WWII Shintoism, Buddhism, Confucianism, and to a lesser extent Taoism, are all still deeply embedded in the culture.

It’s always a bit strange for an atheist like myself to attend all the various religious ceremonies related to birth and death in Japan. Whether you believe or not is beside the point. Showing up though is mandatory, lol.