This is a recurring monthly bill, so a "just sign whatever" choice quietly costs you money every month for your whole stay. Mio doesn't care about vibes — here's the math.
Phone tethering uses the data on your SIM — great if your plan already has a large or "unlimited" allowance, but speeds and caps vary and it drains your battery. Pocket WiFi is a small rental router you carry; typically ¥3,000–4,000/month, no installation, works day one. Home fibre (hikari) is a wired line into your apartment: typically ¥4,000–6,000/month plus a setup/installation fee, with the lowest cost per GB but a real commitment.
| Option | Rough monthly cost | Best for |
|---|---|---|
| Phone tethering (large-data SIM) | SIM cost only, e.g. ¥2,000–3,500 | Light use, one person |
| Pocket WiFi (rental) | ~¥3,000–4,000 | Short stay, no installation |
| Home fibre (hikari) | ~¥4,000–6,000 + setup fee | Long stay, WFH / streaming |
All figures illustrative — actual prices vary by provider, area, building, and campaign. Note fibre adds a one-time setup/installation fee (often several thousand to tens of thousands of yen) that only pays off if you stay long enough to spread it out.
Many home-fibre and some pocket-WiFi plans lock you into a fixed term (commonly ~2 years) and then auto-renew. Cancel outside a short "free cancellation window" and you can owe an early-termination fee — and fibre often adds a separate line-removal / restoration fee when you move out. If you'll leave Japan before the term ends, those fees can wipe out the "cheaper per month" saving.
Mio-style defence: before signing, find three numbers — the contract length, the cancellation fee, and the renewal/free-cancellation month. If your stay is shorter than the term, prefer a no-contract or short-term option (pocket WiFi or tethering) even if the monthly figure looks higher.
Staying under a year, or light use → pocket WiFi or a large-data SIM + tethering. No installation, no removal, no contract trap. Staying 2+ years with heavy use → home fibre, but only after you've read the contract length and the exit fees. The "right" answer isn't about speed brochures — it's about how your stay length lines up with the contract term.