I can't address the first part of your question, but I can talk about the second.

First of all, I have to draw up some warning for myself. There's some possible danger here in treating Buddhism as a unified religion, which it's not. It's as splintered as you would expect a 2500+ year old religion to be, and has changed over time. But I can only speak in generalities in a short summary.

You can make a case that Buddhism does not condemn much of anything. But regardless, Buddhism does not condemn suicide, so your premise is flawed. Suicide in Buddhism is often seen as something negative, and there's a gulf between that and something like the Ten Commandments which strictly condemns certain acts. But, in Buddhism, it's not the act of something that is important, but the mental state that led to it, and the consequences of the action which are important. So more importance is placed on intent and the ends, than on the means.

There are various stories of suicide in the writings of Buddhism. For example, the Jātakas are the stories of the past lives of the current Buddha. Two (three?) of the Jātakas deal with suicide, and The Hungry Tigress Story is probably the most famous of all the Jātakas. In The Hungry Tigress Story, the Buddha, in one of his previous lives, looks down from a cliff and sees a starving tigress about to kill her cubs and eat them. So he jumps down and offers himself to the family. The tigress and her cubs eat him and so he saves the tigress from killing her cubs and saves the cubs from being eaten.

Famous today doesn't mean that it has had the most impact over the course of history. But I'm talking about this story only to show that there is a precedent for showing suicide in a partially or mostly positive light. The most famous depiction of this story also happens to be painted on a panel of the Tamamushi Shrine in Nara, Japan.

Besides the many other writings about suicide, there are also more recent examples of suicide in Buddhism. Buddhist monk, Thích Quảng Đức's self-immolation in Vietnam is just one example of a tradition of protest suicides. There were also ritualistic suicides by monks in Japan and elsewhere, though mostly historical rarities. Although not strictly seen as suicide, one type is self-mummification, which you might have heard about recently with the finding of a mummified monk inside a Buddha statue.

While I'm not trying to say that Buddhism encourages suicide, it doesn't condemn it either. The truth, just like most everything in Buddhism, is somewhere in the middle.

Do you have something more concrete/specific to say about what you think Japan's cultural view on suicide is? Or did you purposely leave it as a open ended question to be answered?

Since Japan's views on suicide have varied a great deal for hundreds of years, I'm going to need a more specific era or I'll have to be incredibly general.

Finally, while suicide is seen as a negative action, it isn't actually condemned in Buddhism. That is to say, you aren't philosophically 'punished' for suicide as one might be in Christian ethical philosophy. In fact, Buddhism generally accepts that self sacrifice that involves suicide in various forms is a positive action.

Shinto is similarly fairly open, doctrinally speaking, to the idea of suicide in the context of great self sacrifice for a greater good/purpose.

Either way, it's hard to answer your question unless you specify if you mean in the modern period (late 20th century, 21st century), World War 2, the industrial period (Meiji), Sengoku Period, classical/ancient Japan, etc.

Finally, especially about the modern era, this is a very contentious issue that is not strictly history since it delves deeply into mental illness, how the mind works, social issues, etc. which are not strictly defined and many still debate about it to this day.

So any answers I do provide are not meant to be read as the authoritative answer, merely my personal perspective on a massive conversation that is still ongoing today.

With all this in mind, I'm happy to answer any questions you have if you could kindly be more specific as to where you would like me to focus. Cheers!

I would Also be interested in how Shinto views suicide if this is an appropriate place to ask that