It would depend on the agreements between the two countries.

If you're in the US, it looks like there's a 12.5% tariff on good from Japan, but I don't know much of anything about importing.

So you live in the US now?

Any goods that are shipped from abroad are subject to duties and tariffs by the Federal Government. And, as you may have noticed, the current administration likes smearing it's duties all over the place. Do not assume anything will arrive with zero percent duty. Look it up.

There used to be an exception for small items, which your cartridges might have applied to, but then jokers like Temu and Shein used that to ship millions of dollars of goods into the US duty free, one small shipment at a time. So now that exemption is more or less gone.

There is still a an exemption if you physically visit a foreign country and come back with small value items. You are supposed to declare it when you come back to the US, but as far as I can tell nobody cares if you do not as long as you are legitimately under the exemption limit. Just keep a list of all items you acquired abroad and be ready to produce it. (Note that key items, like alcohol and tobacco, have their own separate limits, and should probably be declared regardless).

Also, if you live in a state that has a Sales Tax, they likely also charge an equivalent Use Tax on items bought outside of the state and brought in. This even applies to goods bought in a different state in the US. While this is practically unenforceable for many things, when you accept a shipment from abroad it leaves a paper trail and so there is some proof that you received a thing without paying Use Tax on it. Nobody is going to nail you for not paying use tax on a 3DS Smash Bros cart, but if you do a lot it might get someone's attention.

TLDR: Don't smuggle!

You have already asked this question a hundred times already. Your account is 3 weeks old which means you create a new account every time you don't like the answers.

What is wrong with you?