Rakuten Mobile Partner Area Explained: au Roaming Guide

What is Rakuten Mobile's partner area? Explains au roaming coverage, data limits, and how to check whether your phone is on Rakuten or KDDI's network.

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Rakuten Mobile coverage map showing partner area au roaming zones and own network in Japan

Last verified: February 25, 2026 (JST)

New Rakuten Mobile subscribers sometimes see "KDDI" or "au" in their status bar instead of "Rakuten" and wonder if something is wrong. It isn't. You're in what Rakuten calls the partner area—KDDI's (au's) network, which Rakuten uses through a roaming agreement in places where its own towers aren't deployed yet.

Quick Answer: Partner area means your phone is using KDDI's (au) infrastructure via roaming rather than Rakuten's own towers. It provides reliable 4G LTE coverage for calls and data, but 5G isn't available and it's now limited to specific locations—mainly deep subway stations, mountain tunnels, and remote rural areas. Most everyday locations in urban and suburban Japan are on Rakuten's own network.

Related guides: Rakuten Mobile Coverage Guide | Coverage Map: How to Check Your Address | Rakuten Mobile 5G Coverage

Get up to 13,000 points when you sign up → https://www.japanmobileguide.com/referral

What Is the Partner Area?

When Rakuten launched its mobile network, it needed nationwide coverage from day one. Rather than waiting years for its own towers to reach every corner of Japan, it struck a roaming agreement with KDDI (au)—Japan's second-largest carrier—to fill the gaps while Rakuten built out its own infrastructure.

The "partner area" is the portion of Japan still covered by that KDDI roaming arrangement. Your Rakuten SIM works there transparently; calls go through, data flows, and you don't need to do anything special. The phone just connects to KDDI's towers instead of Rakuten's.

Rakuten has been systematically converting partner areas to its own network since launch, and the roaming footprint has shrunk considerably. What remains is primarily:

  • Deep subway station platforms and tunnels where infrastructure installation is expensive
  • Long mountain tunnels (Shinkansen and highway)
  • Remote mountainous areas and small islands with low population density
  • Some underground shopping arcades and basement-level commercial spaces

If you live and work in a standard urban or suburban Japanese city, your daily routine is almost entirely on Rakuten's own network.

What's the Practical Difference?

For everyday use—calls, messaging, browsing, streaming—partner area feels essentially the same as Rakuten's own network. KDDI's 4G LTE is high-quality, and you won't notice degraded performance under normal conditions.

The key differences are:

5G is unavailable. 5G only works on Rakuten's own infrastructure. In partner area, you'll have 4G LTE regardless of whether your phone supports 5G or whether there are 5G towers nearby.

Your status bar shows "KDDI" or "au." This is how you know you're on partner coverage. On iOS, it appears next to the signal bars at the top. On Android, pull down the notification shade or check Settings → About Phone → SIM status.

Data limits. Under Rakuten's Saikyo Plan, historically the partner area came with usage caps, but recent plan updates have eliminated most of these restrictions for domestic use. Consult the official partner area notice for current terms, as these can change.

How to Tell Which Network You're On

Your phone tells you in real time:

  • Status bar: Shows the carrier name. "Rakuten Mobile" means you're on Rakuten's own network; "KDDI" or "au" means partner area.
  • iPhone: Settings → General → About → Network shows the connected carrier.
  • Android: Settings → About Phone → SIM status → Network shows the active network.
  • Coverage map: The official Rakuten coverage map shows Rakuten's own network in pink/red and partner area in orange/yellow. Cross-reference your location with the map to understand which network you're likely using.

Will Partner Area Go Away?

Rakuten has been converting partner zones to its own network across all 47 prefectures since the carrier launched. As of January 31, 2026, Rakuten added new base stations across 104 municipalities in 40 prefectures as part of continued infrastructure build-out.

The trajectory is clear: partner area shrinks every month. What's left will be the hardest-to-reach locations—deep underground facilities, uninhabited mountain terrain—where the economics of tower deployment don't make sense yet. For most Rakuten subscribers, partner area is already a minor footnote in their day-to-day experience.

Should Partner Area Influence Your Decision to Sign Up?

Probably not, unless you regularly spend time in locations where partner coverage is the norm—long commutes through mountain tunnels, work in deep basement facilities, or living in a remote rural area.

For city and suburban users, the more relevant check is verifying that your specific address has Rakuten's own 4G and 5G coverage. Use the coverage map to verify your home address, workplace, and commute. If those show Rakuten's own network in solid coverage, partner area is irrelevant to your experience.

Are You Using Rakuten Mobile?

Rakuten Mobile's Saikyo Plan costs ¥1,078 for under 3GB, ¥2,178 for 3–20GB, or ¥3,278 for unlimited data—with no long-term contracts or cancellation fees. Full English support is at 0800-805-0805. New users who sign up with a referral earn up to 13,000 Rakuten Points.

Get up to 13,000 points when you sign up → https://www.japanmobileguide.com/referral

Frequently Asked Questions

Is au roaming (partner area) included in my Rakuten plan? Yes. Domestic partner area roaming is included in all Rakuten Saikyo Plan tiers with no extra charge. You don't need to activate anything—it works automatically when you're in a partner area.

Can I make calls in the partner area? Yes. Voice calls work normally in partner area using KDDI's 4G LTE network. The Rakuten Link app also functions in partner areas.

Does partner area use more data from my plan? No. Data used in partner area counts toward your plan allowance the same as data on Rakuten's own network.

Why does my phone sometimes switch between Rakuten and KDDI? Your phone connects to whichever signal is strongest at your precise location. Near the boundary between Rakuten coverage and partner area, it may switch back and forth as you move. This is normal behaviour and doesn't affect calls or data sessions already in progress.

Quick Reference

Aspect Details
What it is KDDI (au) roaming where Rakuten's own network isn't deployed
Shown in status bar "KDDI" or "au" instead of "Rakuten Mobile"
4G availability Yes — standard 4G LTE via KDDI
5G availability No — 5G requires Rakuten's own network
Where it applies Deep subways, tunnels, remote rural/mountain areas
Coverage map color Orange/yellow
Data limits Check current terms at official partner area notice

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