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.
It could be his own mother. She might realize that he has become too dangerous and, in a moment of heart - breaking decision, find a way to destroy him. Maybe she discovers a weakness and uses it against him, driven by her love for humanity and the knowledge of the destruction he could cause.
One possible motive could be revenge. Another character might have a grudge against Lucy for something she did in the fictional world, like betraying a group or stealing something precious.
If the Boss gets killed in a Saints Row 3 fanfiction, it would be a huge shock to the story's universe. The Boss is such a central figure, and their death could lead to chaos among the Saints. Maybe one of the lieutenants would try to take over, but it wouldn't be the same without the Boss's charisma and leadership. It could also open up new storylines, like the Saints seeking revenge for their fallen leader.
Brightburn's powers are similar to Superman's but with a malevolent twist. When they interact, it could be that their super strength clashes in a way that causes massive destruction around them. Their flight could lead to high - speed aerial battles, with each trying to outmaneuver the other. And their heat vision could cross, creating intense energy bursts.
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.
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.
Naruto would be shattered. Given his strong sense of justice and his connection to Hinata, whether it's a romantic or platonic one. He would initially be numbed by the shock. But soon, his emotions would erupt. He could go through different stages, from mourning and self - blame (thinking he could have protected her) to a fierce determination to make things right. His actions would be driven by his love and respect for Hinata, and he would not rest until he has either avenged her or found a way to bring her back, if possible.
Well, perhaps in this fanfiction, there could be a plot where a dark curse is placed on Hinata. As the curse takes effect, she gradually weakens until she finally succumbs and is killed. It could also be that a misunderstanding leads to her being in the wrong place at the wrong time and getting killed accidentally.
It could be a long - lost relative of an old enemy. For example, if there was a powerful dark wizard that Natsu defeated in the past, this relative might come seeking revenge and be powerful enough to kill Natsu.