Japan Real Unlimited eSIM Now Live: KDDI Local — Full-Speed vs 10 Mbps?

The unlimited-data choice for travelers heading to Japan just leveled up. Polaris eSIM has launched a KDDI native real-unlimited Japan plan: no total cap, no nightly reset, riding the same KDDI line as Japanese subscribers. Two versions go live together: a full-speed line that never throttles 4G/LTE/5G, and a permanent 10 Mbps line. The 7-day gap is TWD 390, or TWD 56 per day. Which one is for you? Eight concrete scenarios below.

What does "real unlimited" mean, and how is it different from daily-bucket plans

The label "unlimited" actually splits two ways:

• Daily bucket: a soft daily ceiling of X GB; cross it and you throttle or cut off until midnight reset. Pros: a daily roof keeps any single day from spiking. Cons: timezone math is awkward, and once the daily X is gone, the rest of that day cannot serve high-bitrate video.
• Real unlimited (no total cap): no GB cap across the entire validity. Burn 50 GB today and 80 GB tomorrow without any reset. The Polaris Japan plan in this article is the real-unlimited type.

Everything below is about the real-unlimited version.

What KDDI native line means

A native line (Local Breakout) means your phone, on landing in Japan, latches directly onto a KDDI local tower; the packets do not detour through Hong Kong or Singapore. You ride the same line as Japanese subscribers, with the speed and stability of a true local number. For the deep dive on local versus roaming, see this article.

The plan explicitly runs on KDDI 4G/LTE/5G. KDDI is one of Japan's major carriers, with solid coverage on the Shinkansen, across Tokyo's 23 wards, in Osaka, Kyoto, Fukuoka and the other tourist hubs.

Two versions side by side

Both versions sit on the same KDDI native line, both have no total cap, both support hotspot. The only differences: speed ceiling and hotspot allowance. The product page is here, pick the variant at checkout.

Who fits the full-speed version, in four concrete scenarios

1. Tokyo to Kyoto Shinkansen, 2.5 hours of high-bitrate streaming

Inside the Shinkansen, KDDI 5G holds steady from Shinagawa to Kyoto, exactly the length of a 4K feature film. The full-speed version plays through without buffer. The 10 Mbps version forces 4K to drop to 1080p to stay smooth. If long rides are your cinema time, the 56 TWD per day is felt.

2. Family trip with kids on YouTube 4K cartoons

Hotel check-in waits, grandparents passing the baton, Shinkansen rides, rainy-day plan changes. Uninterrupted YouTube Kids or Disney+ 4K is the silent must-have of family travel. The 10 Mbps version stalls on 4K and tops out at 720p; full-speed handles it without fuss.

3. Business travel: video calls, large uploads, live broadcasts

1080p Google Meet or Teams, a 200 MB deck upload, cross-border live commerce at 1080p 60fps — these are upstream-heavy. The 10 Mbps cap chokes upstream noticeably, video drops, big files crawl. Skip the saving on a business trip and take the full-speed line.

4. Travel vloggers backing up tens of GB of 4K every night

Tens of GB of 4K footage to back up to Google Photos, iCloud or OneDrive every night. The 10 Mbps version cannot finish overnight. The full-speed line on KDDI 5G has meaningful upstream headroom; queue uploads before sleep and they are done by morning, no anxiety about losing footage if the phone goes missing.

Who fits the 10 Mbps version, four scenarios

1. IG / TikTok / Reels short-form scrolling

Ten megabits is plenty for short-form video. IG Reels, TikTok, and similar feeds at 720p hold steady. New clips load one or two seconds slower than full-speed but the felt difference is small. Two to three hours of daily scrolling fit comfortably.

2. Pure navigation + chat apps

Google Maps + LINE + Messenger + IG DMs are all far below the 10 Mbps ceiling. A LINE voice call uses well under 0.5 Mbps. Buying full-speed for this profile is wasted budget.

3. Short trips, budget-conscious students or backpackers

A four-day, three-night Kyoto-Osaka dash with photos, social uploads, Google Maps, restaurant lookups; 10 Mbps is genuinely enough. The 7-day TWD 390 saving buys a proper Kyoto wagyu dinner or a fugu meal in Osaka.

4. Hotel-Wi-Fi-heavy travelers, eSIM only for daytime

Some travelers shovel all their heavy use (streaming, cloud uploads, online meetings) onto hotel Wi-Fi each evening; the eSIM only handles daytime navigation and chat. The 10 Mbps cap is plenty here, full-speed would be overkill.

The 56 TWD per day calculation

Seven-day gap is TWD 390, exactly TWD 56 per day to upgrade from "capped at 10 Mbps" to "4G/5G full-speed." How to read it:

• Two to three hours of daily 4K usage (streaming, kids' cartoons, video calls) → 56 a day is worth it
• Mostly social, navigation, photo uploads, lookup → no need to spend the extra 56
• You hate buffering on principle → just take full-speed
• Business trip with stacked meeting blocks → just take full-speed

Hotspot allowance, 3 GB vs 2 GB

Both versions allow hotspot tethering to other devices (a partner's phone, a tablet, a laptop), but the cumulative cap is different:

• Full-speed: 3 GB hotspot total
• 10 Mbps: 2 GB hotspot total

Once the cap is reached the hotspot function gets throttled or paused; your own phone's data is not affected. Travelers who consistently tether a partner's iPad or laptop should pay attention here — a long Shinkansen leg plus a hotel-check-in wait can chew through 2 GB faster than expected.

How to buy and install

Three steps:

1. Open the product page, pick the variant (full-speed or 10 Mbps) and the days (3 to 31)
2. Pay; the QR code email arrives within minutes
3. Scan the QR code, 30 seconds and you are installed. Step-by-step in section 2 of the eSIM beginner guide

Run the eSIM compatibility check first to confirm your handset is supported. If you are still on the fence between the two versions, open the chat in the bottom-right and let our AI advisor Stella read your itinerary and tell you straight whether full-speed or 10 Mbps fits better.