Domestic low-cost airlines will weight all your cabin luggage
TL;DR Peach and Jetstar weigh all cabin luggage as part of the standard process. Be sure you’re under 7 kg per person.
We flew with Skymark, Peach and Jetstar inside Japan.
Skymark didn’t check anything.
Peach and Jetstar were weighing all cabing bags and hand items as part of a standard procedure. Which means, you won’t get through without your bag being weighted, either at check in counter or boarding gates (depending if you have check-in baggage).
Both Peach and Jetstar allowed us to share the allowance between two of us. We put all our bags on a scale and as long as it was under 15.8 kg (7 kg + 0.9 kg margin pp), we’re good, even if any individual bag exceeds 7.9 kg. I felt like staff was our ally there and was genuinely relieved when we passed the check.
You can save a couple of kilos by putting everything you can on you. Hang the camera on your neck, keep headphones on your head, put your jacket on, put small but heavy stuff in your pockets. But for the peace of mind - both yours and the staff’s - just keep your hand luggage light and within allowance.
What happens if you exceed the weight?
I’m used to European airlines, where cabin bag check is a gamble, and it’s usually the size, not the weight. So when taking a domestic flight in Japan, I haven’t even thought about weighing it.
We ended up with something like 10-12 kg per person. Staff suggested to buy extra check-in baggage space for the heaviest bag (it was about 3500 yen, which is much cheaper than I expected).
It couldn’t be paid by cash, only card, and for some reason my Chase MasterCard got rejected, had to pay with my UK Visa card (it’s a good idea to always have a backup card of different type, even if its conversion rate or fees are not great).
After all, the consequences of our carelessness wasn’t bad but I wish I was more prepared in advance. I hope my post will save someone hassle and money.