Because you cannot easily restore Docomo-specific partitions, a failed flash often results in a hard bricked device.
Modifying a Docomo device carries significantly higher risks than modifying a standard Google Pixel or OnePlus device. docomo unlock bootloader top
Standard Android commands like fastboot oem unlock or fastboot flashing unlock are disabled or removed from the boot partition. docomo unlock bootloader top
If your Docomo device is running an older version of Android, you might be able to use a software exploit to gain temporary root and overwrite the bootloader status. docomo unlock bootloader top