Different Brands SIM Free Phones

I'll be visiting Tokyo in 3 weeks time and I intend to buy some new and used SIM FREE phones for my family.
I see that shops carry unbranded phones as well as SIM FREE of phones of different carriers (Like Softbank, Docomo, AU, Rakuten ).

What would be the differance between un branded phone, to a branded SIM FREE phone ?
Are there significant differances between phones of different brands (i.e Softbank, Docomo, AU, Rakuten)?

You mention carriers, not phone brands. Are you asking about phones that are not tied to a carrier? In any case, to get a mobile in Japan generally you need to be a resident (telco act legislation applies). Otherwise, you will be on data only.

Do you need sim-free phones because you're worried that your current phones will incur charges using your current sim card? If that's the case, you can literally just put your phone into airplane mode so it won't use any data at all and you can literally just connect to wifi.

You could even do this by buying a portal wifi device that you can connect multiple devices to it and it would be a lot cheaper than to try renting sim-free phones phones from a carrier, since as JapanCustomTours said, it may not be possible to get an actual phone with a phone number unless you're living in Japan.

I've personally done the first option of using my phone from my country and just switching off data and using a portal wifi device. Worked extremely well.

Sorry. I think my question is not clear enough.
I am going to buy SIM FREE phones to be used at my country, after I leave Japan.
So the question is actually
"Are there significant differances between phones of different brands (i.e Softbank, Docomo, AU, Rakuten)?"
Thank you

Are there differences between the phones themselves if they come from a carrier such as Docomo or Softbank? Nope.

I used to work in a phone store and all the phones are the same. The only difference is if they're unlocked or not.

"Are there significant differances between phones of different brands (i.e Softbank, Docomo, AU, Rakuten)?"
Yes, the three main carriers sell the phones people want, and they are sim-locked (like apple or samsung), and usually sold on contract. Getting them unlocked, those store people will lie to you and say it is impossible. At best, you can point them to a regulation (not a law) and for a fee they might take a few weeks to do it. (as an aside, I have an AU phone I don't use on the network wifi only - and the AU software is embedded deeply into the phone - nothing to do with brand of phone, all about the carrier)
If you want an unlocked phone, your choice of brands is really poor (I want to use a different word here, but keeping polite). I personally don't want an Oppo phone or one of the others relegated to the weird shelves away from the three big companies - I am thinking specifically of the layout in the big camera/electronics stores.
Is the situation better now than when I last checked? You'll find out pretty quickly.
Because of my requirements for an unlocked phone, I don't buy my handsets in Japan. That way I can also actually get the model I want, at a lower price, and without having to deal with the three main companies (for example, I wanted an S10e, but that model was not only not sold in Japan, the Japanese Government did not support it for official software where the S10 and S10+ were both supported). BTW, I spend around 1,000 yen a month on my phone contract in Japan (voice plus data).
The other point to be aware of, you may not actualy save much, and getting a Japanese phone covered for repairs in another country is a consideration. Different countries, different models.

When it comes to SIM-free phones, the main difference between unbranded phones and branded ones (like Softbank, Docomo, AU, or Rakuten) is often the carrier-specific software or settings that may be included with the branded phones. Unbranded phones typically don�ft have any carrier logos or software, giving you a more neutral experience. On the other hand, carrier-branded phones might have pre-installed apps or features specific to that network, but they�fre still unlocked and can be used with any SIM card.

Unbranded SIM-free phones are not tied to any carrier, making them more versatile for use with any network. Branded phones from carriers like Softbank or Docomo are also unlocked but may have carrier-specific apps or settings. The main difference is usually in software, not performance, so if you want a simpler option, unbranded phones are a good choice.