Well, Harry may have realized that Sirius is his godfather, which means there's a special bond already. He might think that living with Sirius would give him a proper family environment, filled with love and understanding, unlike what he has at the Dursleys' place. Also, Sirius has a rebellious and free - spirited nature that Harry might be attracted to. He could hope to grow up in a more exciting and accepting atmosphere.
Maybe Harry has some new information about a greater threat that would also endanger Voldemort. So, he asks Voldemort to save him so that they can join forces against this new threat. Like a new dark entity from another dimension that is coming to destroy the wizarding world, and Harry figures Voldemort wouldn't want to lose his own power base.
Sirius would probably be overjoyed at first. Harry is his godson and he cares deeply for him.
One possible reason could be that Naruto feels he has become a threat to the village or his friends in some way. Maybe he has some sort of dark power within him that he can't control and he believes Sasuke is the only one strong enough to stop him. Another reason might be related to a prophecy or a greater threat that Naruto thinks his death can prevent, and he trusts Sasuke to carry out this difficult task.
One possible reason could be extreme guilt. Maybe Naruto has done something he believes is unforgivable, like accidentally causing the death of a beloved friend while in a fight. He might think that death is the only way to atone for his mistake.
One reason could be extreme despair. Maybe he has faced so many hardships and losses that he feels there's no way out. For example, if he has lost many friends in battles against powerful foes and he blames the gods for not protecting them better.
It might also be due to a sense of hopelessness. If he's faced with an enemy that seems truly unbeatable and he fears the destruction of the village or his friends, he could ask to be killed to prevent further harm. For example, if there's a powerful villain who has Naruto's friends hostage and the only way to save them is by Naruto sacrificing himself.
Perhaps he has been through some sort of mental and emotional breakdown. Maybe he has lost too many battles, seen too many friends die, and he feels that he is a burden or that his death would somehow bring peace to his troubled mind. It could also be related to some prophecy or dark secret he has discovered about himself that makes him think death is the best option for everyone.
One possible reason could be that Harry has a deep love for the characters in the fanfiction. Maybe he has formed an emotional connection with them and wants to see their romantic storylines continue. For example, if it's a story about his favorite character falling in love, he doesn't want that beautiful relationship to end. Another reason might be that he enjoys the world that the fanfiction has created. The romantic elements add a certain charm and depth to that fictional world, and without them, the story seems incomplete to him. Also, it could be that he has been following the fanfiction for a long time and has grown accustomed to the romantic plot, so he wants it restored.
One reason could be Harry's impulsiveness. Harry often jumps into dangerous situations without thinking, and Sirius, being his godfather and having a protective nature, would shout at him to make him realize the risks. For instance, if Harry decides to go after a Death Eater alone.
Naruto might be longing for a motherly figure in his life. He has always been alone and has seen how others have mothers. Tsunade, being a strong and caring woman in the village, could be someone he looks up to and wishes to have as a mother.