Flashing takes ~5 minutes. You’ll see:
After an OTA update failure or a bad root attempt, the phone may hang on the Sony logo. Flashing the stock .ftf restores the original system files. Flashing takes ~5 minutes
Steps: Open FlashTool → Tools → XperiFirm → Select 502SO region (Japan, SoftBank) → Download. Flashing takes ~5 minutes
The is the specific model released for the Japanese carrier SoftBank . Using the wrong firmware on this device can be disastrous. Flashing takes ~5 minutes