One possible scenario could be that he is killed in a lightsaber duel by a powerful Sith opponent. Maybe this new Sith has some secret technique that Anakin couldn't counter.
One possible scenario could be that Natsu is killed in a battle against a powerful and unexpected enemy. Maybe a new dark mage appears with powers that can overpower Natsu's fire magic.
One possible scenario could be a power imbalance. Maybe Sasuke discovers some new, extremely powerful jutsu that Naruto has no defense against. For example, a jutsu that can nullify Naruto's chakra or attack his spirit directly. Another possibility is a miscommunication or a breakdown in their relationship. If Sasuke believes Naruto has betrayed him in some way, his anger could lead him to kill Naruto. However, this goes against the core of their bond in the original series.
In such a fanfiction, one possible scenario could be that Gladion gets involved in a battle against a powerful and malicious Pokemon trainer. The trainer's Pokemon might use a super - powerful attack that Gladion's Pokemon can't withstand, and in an attempt to protect his Pokemon, Gladion gets caught in the crossfire and is killed. Another scenario could be that he stumbles upon a dangerous, secret organization within the Pokemon world that doesn't want their secrets exposed. They might target Gladion and assassinate him to keep him silent.
It could be a new and powerful dark side user. This character might have emerged from the shadows, having trained in secret, and their sole purpose is to take down Anakin as he is seen as a threat to their plans for galactic domination.
There are also fanfictions where Anakin gets hurt in a ship crash. The ship could be attacked by enemy forces, and when it crashes, Anakin suffers various injuries like a head wound and broken ribs.
Well, in a fanfiction, he might be killed by his own hubris. Let's say he continuously underestimates the power of human ingenuity. A group of scientists manage to create a device that disrupts his energy source. While he's weakened, the military launches a full - scale attack using advanced weaponry specifically designed to target his unique physiology. So, his overconfidence in his invincibility leads to his downfall.
Some fanfictions might explore a situation where Anakin is being manipulated by a powerful dark force or a Sith Lord. This dark influence makes him see Obi - Wan as a threat to a grander plan. So, he kills Obi - Wan as part of this dark scheme, not fully in control of his own actions. And this can lead to a lot of complex emotions and plot developments later in the story, like Anakin's further descent into darkness and how the other characters react to Obi - Wan's death.
One possible scenario is that Anakin might get inspired by the unique battles and combat strategies depicted in the fanfiction. He could start thinking about how he would handle those situations in his own way, given his skills as a Jedi and later as Darth Vader.
One possible plot development could be that his friends immediately launch a rescue mission. They might use their unique skills and resources to track down the kidnappers. For example, if Obi - Wan is involved, he could use his Jedi mind tricks to interrogate possible informants in the underworld.
One possible scenario could be that the Dursleys, out of their long - held hatred and jealousy, manage to poison Harry's food. In the fanfiction world, they might find a way to obtain a powerful and undetectable poison. Another could be that they stage an 'accident' like a fire in his room while he's asleep. They could block his escape routes and let the fire consume him.