Hanami
So, we now know about 42. However, that is not a thing for everyone. For example, Japanese avoid this number, because, when pronounced "four-two" (shi ni, 死に), it reminds people of dying.
Instead, Japanese use this time in spring to celebrate the Hanami cherry-blossom season, when Sakura (cherry) trees offer spectacular enhancements of already spectacular views and people gather in parks for picnics with their co-workers and friends
By April, it reaches Sendai, north of Tokyo, with nearby coastline beautifully dotted by numerous pretty little islands (e.g. in Matsushima).
By May, the wave reaches the northern-most island of Hokkaido and then it is over, because there are no more islands to the north.
Note: The Kuril Islands, to the north, which used be Japanese, are Japanese no more. The ownership was always somewhat shifty, but in 1875 Japan and Russia agreed that Japan will give Russia the big island of Sakhalin and Russia will recognize Japan's ownership of the set of much smaller Kurils. Well, at the very last minute of WWII, when Japan was on her knees, Russia renounced the Soviet–Japanese Neutrality Pact that kept them at peace until then, invaded the islands and never gave them back. Instead, they ethnically cleansed the population (well, "repatriated" to Japan) and took over everything. Now they have installed there various missile systems, so they really mean to stay. 75 years on, Japanese are still pretty pissed about the whole situation. When I was there (many years ago), in eastern Hokkaido, where the closest Kuril islands are visible to the naked eye, there were demonstration of agitated people carrying banners about the issue. Of course, by now, Russians think all this is rightfully theirs, so Russian people now protest, too: against the idea of ever negotiating with Japan and against the perceived danger of handing over this "native Russian land".
Back to those sakuras.
But what is most special about the time is really the "festival" of Hanami, when everybody streams into parks, alone or in pairs or in groups of friends or coworkers. They spread out a blanket, have some bento and sake and yap, chat and enjoy... Poorer folks, like the student crowd, especially in Kyūshū, will drink shōchū instead of sake, because it is stronger, cheaper, and, well, after a while you kinda get used to it.
The sakura trees in the parks are often arranged to have flat, wide crowns to produce a spanning canopy. My favourite moment was when we climbed, with a couple of friends, on top of one of these trees and sat on the flat top, as if it was a huge carpet of never ending cherry blossoms. We spend there the whole night, drinking, chatting, cherishing the moment.
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Note: interestingly, the Hanami festival is not the only Hanami in Japan. The Japanese enthusiasm for nature and its preservation is also expressed in the homonymous manga character of "Hanami" (but spelled 花御, roughly meaning "go flower", and not like the festival, 花見, roughly "see flower").
Less known than the festival, but still popular as a character in Jujutsu Kaisen, the best-selling manga series of all times, Hanami is an "undead born of humanity's fear of forests", who is so displeased with the plunder people inflict on nature that, as a solution, he decided to eliminate the contaminant, humanity, altogether. But more about that later ... :-)