Docomo Samsung devices, such as the Galaxy S21 SC-51B, follow a relatively structured but still challenging path. The standard procedure includes:
Incorrectly executing unlock procedures—especially with unofficial exploits or paid tools—can result in a "bricked" device that is unusable. This risk is amplified with Docomo phones because most official unlocking methods do not apply, forcing users to rely on experimental exploits.
If you plan to use your unlocked Docomo phone on another carrier, note that bootloader unlock SIM-unlock your device. These are separate security mechanisms. SIM unlocking requires either: docomo unlock bootloader install
These devices are almost exclusively targeted at the Japanese domestic market. Their bootloaders are locked with proprietary encryption keys, and there is virtually no developer community support. Unlocking these is generally considered impossible unless a major, device-specific security exploit is leaked. 2. Prerequisites and Essential Tools
NTT Docomo is one of Japan’s largest carriers. Historically, Japanese carrier-branded smartphones (like the Galaxy, Xperia, or Sharp Aquos series sold by Docomo) come with a locked bootloader, preventing users from installing custom recoveries, rooting the device, or flashing custom ROMs. Docomo Samsung devices, such as the Galaxy S21
If it says Bootloader unlock allowed: No , standard fastboot commands will fail. You must use paid exploit software or server tokens to force an unlock. For Google Pixel Devices
If you need to return to stock (e.g., for warranty or selling): If you plan to use your unlocked Docomo
Many newer Docomo devices (post-2021) use hardware-level verified boot (e.g., Samsung Knox, Sony TRUSTZONE). On these, unlocking the bootloader is either impossible or will permanently break features like:
If official unlock supported:
If your ROM requires a separate Google Apps package, repeat the installation step with the GApps zip immediately after flashing the ROM, before rebooting.