Adrien might become a vigilante. He could use his night vision to patrol the city at night, looking for criminals and helping those in need. His ability would give him an edge over the bad guys who are used to operating under the cover of darkness.
One possible explanation could be that it's a result of some sort of genetic experiment gone wrong. Maybe his parents were involved in a top - secret project, and Adrien ended up with this unexpected night vision ability as a side effect.
Maybe they embark on a journey to rescue a captured demigod. Along the way, they face various challenges like crossing a dangerous river filled with sea serpents. Percy's knowledge of the water and his brother's problem - solving skills (again, depending on how the fanfiction portrays him) would help them get through the obstacles.
In fanfiction, Naruto and Kaguya could embark on a journey to rewrite the history of the ninja world. Since Kaguya was at the origin of many of the world's problems, they could try to fix things at the root. This would involve traveling through time, perhaps, and facing many challenges along the way. They might have to battle against ancient enemies that Kaguya herself once created or deal with the consequences of her actions in the past in a more hands - on way.
Harry could have adventures where he tries to help his parents' ghosts pass on to the afterlife properly. This would involve solving mysteries about their untimely deaths. Along the way, he'd meet other ghosts with their own stories, and they could join him on his quest. He might also find ancient spells that can interact with the ghostly world more fully during these adventures.
They could have an adventure in a parallel universe. In this universe, the rules of power and combat are different. Trunks and Pan would have to adapt quickly to survive and find their way back home. It would be a story full of new challenges and discoveries for both of them.
An adventure where they have to stop an evil force that is threatening both of their worlds. Naruto could bring his knowledge of sealing jutsu to prevent the evil from spreading, and Noire could use her leadership skills to gather allies.
They could have a mini - adventure within the quarantine zone. Maybe they discover a hidden room in the compound that has some sort of mystery element. For example, it could be a room filled with old technology from the early days of S.H.I.E.L.D. that they have to figure out how to work. Or they could have a cooking adventure, with Thor trying to make Asgardian food and everyone else either being horrified or pleasantly surprised by the results.
They could go on a quest to find a powerful artifact that has the potential to destroy both their worlds. Bruce's detective skills and Percy's demigod powers would make them a formidable team. For example, they might have to search for an ancient Atlantean relic that has been corrupted by dark magic.
If Hermione was Oliver's sister in fanfiction, they could have all sorts of adventures. For one, they could team up to investigate strange happenings around Hogwarts that seem to be affecting the Quidditch games. Since Hermione is smart and Oliver is observant in the Quidditch field, they'd make a great team. They might also go on a quest to retrieve a lost Quidditch trophy that has some sort of magical power. And perhaps they'd get involved in a mystery involving a cursed Quidditch broom that is causing trouble for the players. Their combined skills would surely help them solve these problems.
One possible adventure is that they travel to a different dimension. The goblin friend has a special ability to open portals, and they end up in a dimension where magic works differently. There, they have to find their way back while also helping the local magical beings who are being oppressed by a powerful entity. Or they could go on an adventure to a hidden island where a powerful magical creature lives, and they need to get an ingredient from it to make a potion that can save Hogwarts from a curse.