eSIM (recommended): Ubigi, Airalo, or Mobal. Activate before boarding. 10GB plan ~RM90.
Free WiFi: 7-Eleven, Starbucks, train stations. Download "Japan Wi-Fi auto-connect" app.
Pocket WiFi: Rent at Haneda if group travel (¥500-900/day). Unlimited data, share with 5 devices.