If a person's parents didn't name him/her, does this make him/her immune to Death Note? What would a Shinigami contractor see looking at this specific person?
By the way, nicknames don't count as real names according to this post.
How to Use: IX
- The Death Note will not affect those under 780 days old.
How to Use: XXX
- The names you will see with the eye power of a god of death are the names needed to kill that person. You will be able to see the names even if that person isn't registered in the family registration.
The name to be written in the Death Note to kill a person isn't relevant until the person turns 780 days old. Moreover, even if a person changes his name and/or uses aliases multiple times during his life, there's only one name which can kill the person, and it is known to the Shinigami (as well as a human who has the Shinigami eyes).
From this, it appears that for each person, the name which can kill him is decided at a certain point in his life, and then it is never changed. Since the person has to be "killable" on the 781st day of his life, this "christening" (for the purpose of the Death Note) happens before that day.
Further to avoid confusion, this christening is presumably done by the Shinigami King or automatically handled by the Death Note system somehow. Of course, who would go through the trouble of choosing a unique name for every person? Thus, for simplicity, the person's official name is chosen for this purpose.
Most people are given some official name by the time they are 780 days old, so this won't cause a problem. For the rare cases where a person doesn't have a name by that day, the Shinigami King or the Death Note system presumably picks some random name on the 780th day (to satisfy the rule IX/1).
With this arrangement, the Shinigami and humans having the Shinigami eyes know the name required to kill the person. Humans who own the Death Note but do not have the Shinigami eyes cannot kill the person using the Death Note because they don't know the name required to kill him.
Obviously the name that kills you is the one that whoever, disregarding their relationship to you, be it blood relation, friend of family or mere acquaintance, gives to you before the time period of immunity to Death Note wears off. If for whatever reason it may be and absolutely no living being names you in said safe period, the second that said safe period runs out the Death Note's king of gods of death shall pick a name of his choosing and then assign it to you, this shall then be from that moment on and until the day of your death the name that will cause your destruction at the hands of the person writing said name into any Death Note that has come into their possession by whatever means that led them to it/them.