Once you modify the recovery or boot image, you will no longer receive official security patches from Docomo.
If your device shows "Yes," follow the universal Android unlocking process: docomo unlock bootloader top
: If you are looking for the "top" way to do this, it usually involves paid third-party services (like qUnlock or S1 Unlock) rather than free software, as Docomo devices do not support the official Sony or manufacturer unlock codes [2, 4]. Once you modify the recovery or boot image,