Actually, I think they'd have a large and active gun culture if they'd let themselves...
Nah, Japanese gun laws are the strictest in the world. If you think Canadian licensing is harsh, the procedure to aquire a firearm in Japan is as follows;
1) Must attend a safety class and pass a written exam. Attendance is mandatory.
2) A second exam tests the applicant's marksmanship as well as range safety and rules.
3) A full mental health checkup at a recognized major hospital is required. A physician / psychologist must sign off for the applicant.
4) A full criminal background check of the individual, once that is completed a full criminal check of the following; any spouse, all parents (maternal and paternal), and all legal dependents.
5) A full political background check is required. If the individual or any in his or her immediate family have any affiliation whatsoever with any recognized extremist groups then the application is denied.
Once all that is done, you may legally acquire a shotgun for sporting purposes only.
Now of course, there hasn't been any such 'massacre' in Japan although I can think of a effective if morbid reason why this is.
If you've grown up in an older fashioned Asian family, the pressures to perform are very high. If a child fails to meet expectations... Well the parents won't say it out loud but the expectation is you either shape up or die with dignity and spare the family any further problems. Suicide isn't considered a disgrace on anyone's part. Police take the same attitude; if it looks like suicide, they're more likely to just to write it off (they're usually thorough though).