They are both saved by the clause on page XXIX, where it states “You cannot kill humans at the age of 124 and over with the Death Note”. The suicide clause would still end them completely – Kakuzu can output more firepower than his hearts can handle probably handle and even though Hidan is supposedly immortal, Kishimoto did confirm that he can die from malnutrition.
To clarify, it is not because that they are immune to heart attacks (even though they are – Hidan is completely immune to dying and Kakuzu has five hearts so if he gets a heart attack he can literally throw the heart away and use another one ). I was specific to mention that almost everybody in these universes would die.
Some ninjas can level mountains and continents, so what’s to say they can’t kill themselves? The same goes for One Piece and it’s universe that’s chock full of heavy hitting attacks, and I’m not even going to ask the question of “what happens if Saitama punched himself at full power”. Sadly for them, a lot of ninjas, pirates and heroes have techniques that have EXCEPTIONAL killing potential. If the order of the death note is “you must end your own life”, characters will likely use their strongest technique that can maximize the chances of them being dead. These fictional universes have plenty of dangerous techniques that can guarantee a kill if self-inflicted. It is, therefore, not something unbelievable to think of.” Basically, all humans are thought to possess the ability to commit suicide. On page X, the following statement is present: The capacity for medical ninjutsu to undo heart attacks is unknown (maybe extremely talented medical specialists like Sakura or Tsunade could maybe undo the effects of a heart attack, but we can’t say for sure), but there’s another way: suicide. As long as they have a beating heart, I say it’s fair game for the death note to take their lives. They may be superhuman, but they are still human. There are humans that reach the power level of gods, but they are not gods. This means that throughout the eternity of death note usage, no human in the universe of death note has ever survived from having their name written down. On page VI, it states that the specific scope of the conditions of death are not known: meaning that even the gods of death do not know the extent of killing potential the death note has. This is because of the simple fact that despite being powerful, land-bending ninjas or pirates or superheroes, they are still fundamentally human.
Naruto, Luffy, Saitama and almost everybody in these universes will most likely die to the death note. Naruto Uzumaki, Monkey D.Luffy, and Saitama Without further ado, let’s begin the execution. If there’s some question as to that person’s possibility of survival, I’ll cover it. I won’t be making Light execute someone like Yukihira Soma. I won’t be naming the obvious answers where the target is sure to be dead. I’ll also be naming down the names that may spur a unique reaction from the death note.
Just for the sake of clarity, let’s set the exact scene as follows. What does that say for humans like us, with only a short amount of time to figure out what it can or can’t kill? Even someone with the intellectual capacity of Light had to undergo some degree of trial-and-error, so we can’t say that we have definitive yes/no answers. The Shinigami themselves, the gods who literally owned the notebook for eternity, still do not know the full scope of the death note. To be honest though, the death note is a giant playground of assumptions. All 64 pages of the death note’s rules will be taken into consideration as we determine the extent of the death note’s killing potential. We’ll be following the death note’s own set of rules and using logic and reason to come to our conclusions as to if the target can be killed or not. Let’s look at one of the most overpowered weapons in all of anime and put it to the test. What can the death note kill? Is there anything the death note can’t kill? What kind of limitations exist? If it’s taken out of its own universe, what kind of loopholes arise? It’s just as simple as writing down a name and waiting forty seconds? Maybe in the universe of Light and L that holds true to some extent, but let’s take the death note out of its comfort zone and see if it can tackle the behemoths of fiction.