A possible plot is that Mei is kidnapped by a rival nation in an attempt to gain information about her village's defenses. Naruto embarks on a solo mission to rescue her. Along the way, he has to face various traps and enemies. When he finally reaches Mei, he has to protect her from the captors who are trying to kill them both to cover up their crime. Naruto uses his Sage Mode to overpower the enemies while shielding Mei from harm.
In a fanfiction, Naruto could protect the Kyuubi when a new, unknown enemy emerges from a different dimension. This enemy has the ability to separate Naruto from the Kyuubi, which would be disastrous. Naruto has to not only fight this enemy physically but also strengthen his mental bond with the Kyuubi to prevent such a separation. He might also have to seek help from old friends and mentors, and together they form a shield around the Kyuubi to keep it safe.
One plot idea could be that in a new, dangerous mission, Naruto is constantly by Sakura's side, shielding her from attacks with his quick reflexes. Another could be Naruto using his newfound jutsu to create a protective barrier around Sakura when she's in a vulnerable situation during a battle against a powerful enemy. And perhaps Naruto fakes his own death to draw out an enemy who has been targeting Sakura, and then reveals himself at the last moment to save her.
One idea could be that Peter gets into a situation where he's facing a powerful new villain that his usual powers can't handle. Hulk steps in, using his brute strength to fend off the attacks while Peter tries to figure out the villain's weakness. Another plot could involve Peter being in a dangerous location, like a collapsing building, and Hulk arrives just in time to shield him and then help him rescue others trapped there.
In a fanfiction, Sakura could be kidnapped by a group of rogue ninjas who want to use her medical skills for their own evil purposes. Kakashi gets wind of it and embarks on a solo rescue mission. Along the way, he has to fight through various traps and enemies. When he finally reaches Sakura, he has to protect her from the final boss - like rogue ninja while also helping her regain her confidence after being held captive.
One plot idea could be that in a world where dark forces are targeting Hermione for her intelligence and her role in the fight against Voldemort. Snape, due to his complex relationship with the Order of the Phoenix, and Lucius, perhaps having a change of heart after seeing the true brutality of Voldemort's regime, team up to protect her. They could hide her in an old, magically protected manor that has been in Lucius's family for generations. Snape uses his skills in potions to create protective elixirs for her, while Lucius uses his knowledge of dark magic to set up wards that only they can pass through.
Well, a possible plot is that Sasuke discovers a conspiracy against Sakura's pregnancy. Some mysterious group might be planning to use her unborn child for some dark purpose. So, Sasuke has to use his skills and intelligence to uncover the conspiracy and protect his family. Or perhaps, Sasuke has to deal with the internal politics of their village while protecting Sakura. The village elders might have different opinions on Sakura's pregnancy and Sasuke has to stand up for his family.
A possible plot is that Baldroy defends Ciel from a powerful magician who wants to use Ciel for some dark ritual. Baldroy, being the loyal servant, stands in the way and manages to hold off the magician long enough for help to arrive. Another could be that Baldroy protects Ciel during a trip through a dangerous forest. He fends off wild animals and traps set by bandits. Also, he might protect Ciel from a slander campaign within the aristocratic circles. He could gather evidence to prove Ciel's innocence by using his network among the servants.
A plot could revolve around the community's reaction. Some in the community might be happy for them, while others could be judgmental. Alphonse and Mei have to deal with this external pressure while also preparing for the new arrival, like finding a proper home and getting the necessary supplies.
Well, perhaps there's a new demon in the land that specifically targets those with spiritual powers like Kagome. Sesshomaru, who has a certain level of disdain for most humans but also a sense of the greater good in the world, steps in to protect her. They could end up on a journey to find the source of this new demon threat. During this journey, Sesshomaru teaches Kagome some of his combat techniques to help her defend herself better, and Kagome, in turn, shows Sesshomaru the value of human emotions and connections.
A more complex plot might involve Tayuya being captured by an enemy group and Naruto being the only one who can rescue her. Along the way, Naruto discovers some secrets about Tayuya's past that change his perception of her, and she in turn realizes that Naruto is not just a simple - minded ninja as she initially thought. As they escape from the enemy, they form a bond that is both unexpected and deep.