We know that if you kill a person via a disease, the Death Note isn't limited to the 23 day rule. Now those who have watched death note know, you can manipulate a person to an extent. So my question is, could I write something like this?
John Doe, Diabetes. Obeys every command from the person he knows as J, till he dies.
Could this work?
There are different ways to interpret this question. So let's break this down
John Doe, Diabetes. Obeys every command from the person he knows as ''J'', till he dies.
SO according to rule 23
If you write die of disease like before with a specific disease's name, but without a specific time, if it takes more than 24 days for the human to die the 23 day rule will not take effect and the human will die at an adequate time depending on the disease.
So the first part of your question
John Doe, Diabetes.
works fine and the disease would take a natural course of action.
But here is the catch. You cannot let another person control the user as easily as you think. In the second sentence
Obeys every command from the person he knows as ''J'', till he dies.
You have entered the name 'J' and would kill the person named as 'J' using a heart attack.
Also the line states "Every command" that 'J' gives. SO "every" command could also include that 'J' orders john doe to do things he would not like to do or 'J' could order 'Jon doe' to kill others which is not possible. According to TV tropes
The first is that the Death Note can only kill one person per name. If it brings harm to anyone else, the person will just die of a heart attack. Also, aliases don't work, period. The Death Note doesn't know who L or Kira or Wedy or Aiber or Near or Mello or anyone else with an alias are. Real names only. However, you could write something like "Report Siht. Demolishes a hotel, then subsequently dies." and then write "L Lawliet. Crushed by falling debris as his hotel is demolished." As long as two names are written, they are able to interact.
So there is a limit of how much you can control and you cannot pass the control to someone else without killing them(since you wrote 'J' in death note already). So you statement in the death note would fail and would kill 'J' with a heart attack and also kill 'John doe' with a heart attack as the "Obeys 'every' command" is ambiguous.
EDIT: In respect to the comment by Dark Yagami.
What works:
John Doe, diabetes. Eats fries and gummy bears, cheats on his girlfriend
would work and you can control them as long as you want (at least till they die of diabetes).
What does not work:
John Doe, diabetes. J, diabetes. John Doe obeys every command of J
won't work. Because you transfer control of power to change the lives of other people (in this case J could ask John Doe to kill someone or make John Doe do something impossible like fly to California from Japan in 2 mins. You cannot give an ambiguous command or control of other people's lives in the Death Note as the death note would just kill John Doe with a heart attack and J with diabetes in the above case.
One thing you guys must understand is, Death Note does not transfer the ability to control the lives of anyone other than the ones in Death Note. So you cannot make someone do something they would never contemplate. So handing over life of someone to another person is impossible for death note to do.
Source: http://tvtropes.org/pmwiki/pmwiki.php/Headscratchers/DeathNoteRulesOfTheDeathNote
I have watched the series only once and I am sure it is clearly stated in the series that it is absolutely possible to control a person's actions and manipulate him to do anything at all as long as it is physically possible for that person to do so.
But I don't really think if that command is going t work. You see, death note only kills a person and you can make a person do some stuff before he eventually dies. There might be a time limit for manipulating the person before he dies but I am not sure about that. I think I read something about this kind of stuff in the rules that appear in the series.
But there's another thing. For instance, he wrote Diabetes. The death note only makes the person do things that are physically possible. Otherwise, he dies of a heart attack.
Now what if the person is fit and doesn't consume a lot of sugar? Death note is only supposed to alter a person's state of mind and make him to stuff. But bringing about a biological change in a person sounds kind of impractical to me, save for the heart attack though. That's the default case scenario.
tl;dr: This will not work and John will die of diabetes at an adequate time. In the off chance that John is so healthy that it would not make sense for him to die of diabetes, he will ironically die of a heart attack instead.
Before I start quoting the rules, let us go back to the beginning. In chapter 6, when Light just got his Death Note, he was as curious as you are right now and did similar experiments to the question you have been having. In one of the failed experiments he requested a prisoner to write down the words I know L distrusts the police. Light almost thought it would work, but he guessed that it would be impossible for him to make people have thoughts they would never have. In other words, even with the Death Note, Light could not do the impossible, whether it would be physically impossible (eg: travel to Paris in 30 minutes) or mentally impossible (eg: draw a picture of an unknown person or write down something you would not naturally think of).
So coming back to your question, where John has to obey every order J gives him. It would be impossible for John to be thinking about obeying every command J tells him. Therefore, similar to what happened to the prisoner, the situation of death would become void and only the cause of death would occur as written down.
Relevant rule: Also, after writing the cause of death, even if the situation of death is written within 6 minutes and 40 seconds in the human world, the situation will only occur to the victims whom it is possible. For those where the situation is not possible, only the cause of death will occur. HTU:LVI
This would make the situation of John's death impossible, but not the cause. Therefore John will still die of diabetes, with nothing more specified about his death. Unless he is medically unlikely of gaining diabetes, as mentioned earlier. In that case, he will die of a heart attack.
Relevant rule: In the occasion where the cause of death is possible but the situation is not, only the cause of death will take effect for that victim. If both the cause and the situation are impossible, that victim will die of heart attack. HTU:LV
Since you did not specify a time of death, the 23-day rule was bypassed and John will die at an adequate time needed for the disease to take effect.
Relevant rule: If you write die of disease like before with a specific disease's name, but without a specific time, if it takes more than 24 days for the human to die the 23 day rule will not take effect and the human will die at an adequate time depending on the disease. HTU:XXVIII
You can write that but the person would die in 10 seconds because you didn´t put the time when he dies. (I think it was 10 seconds)
