I would assume otherwise (but I may be wrong). Usually (in most countries, in most situations) you clear immigration and customs (which means collecting your bags) in your first port of entry. At that point, you’re released into the general area and have to go re-check your bags for the onward flight. I assume you’re on the JL flight (or the AA codeshare on that flight), so maybe check with the airline.

The airports usually have wifi rental facilities in the terminal but those are normally landside and would be much less likely to be in the transit area. You can rent them online and have them delivered for airport pickup (usually at a convenience store (perhaps Lawson) or post office) or delivered to your hotel etc. so it’s there when you arrive. Obviously airport pickup is preferable if you want to get online asap. Try iVideo. We rented their Softbank 601 unit last time we were in Japan - it worked fine. They provide a return envelope so you just drop it in the mail before you leave. If you don’t already have one, you may also want to rent a power bank from them; the wifi unit will probably last about 8 hours or so if you have it turned on all the time, so will probably start to run out of power in the late afternoon (depending on what time you start in the morning...). The power bank can obviously also be used to charge your phone etc. when you’re out and about.