Unlike international models where you can toggle "OEM unlocking" in developer options, docomo's firmware usually disables this feature entirely, making it impossible to install custom ROMs or gain root access through standard methods. Why docomo Devices are Restricted Carrier Policy
Here is the current "Top Tier" status for DoCoMo unlocks: docomo unlock bootloader top
If you have an unlockable Docomo phone (check XDA Developers forum for your exact model), here is the ranked workflow: Unlike international models where you can toggle "OEM