A possible plot for a Harry Potter shower room fanfiction could be that the shower room is haunted by the ghost of a former student who was wronged in that very place. Harry, being the brave one, decides to communicate with the ghost and find out what happened to help it move on. Another idea is that the shower room's water has some special magical properties that start affecting the students' magical abilities in unexpected ways. For example, it makes Neville suddenly able to perform advanced herbology - related spells. And a third idea is that the Marauders once hid a prank - related map in the shower room that Harry discovers, and it leads him on a wild adventure around Hogwarts.
One idea could be that a group of students discover a hidden section within the Room of Requirement that has a time - travel portal. They then have to decide whether to use it to change certain events in the wizarding world's history. Another could be that the Room of Requirement creates a magical garden full of plants that can talk and offer wisdom. And a third idea might be that the room turns into a training ground for a new and dangerous form of magic that the students have to master to save Hogwarts from a new threat.
A plot could be that Harry and Hermione are looking for a way to bring back some of the lost memories of the students who were affected by a powerful forgetfulness charm during a battle. In the Room of Requirement, they find a magical device that can restore memories, but they have to go on a quest within the room to find the power source to activate it. Another idea is that they use the room to train for a magical tournament that's different from the Triwizard Tournament. They face all kinds of magical challenges created by the room itself, and in the process, they grow closer as friends and develop their magical skills even further.
One idea could be that the characters accidentally mix up their lockers in the locker room. They then have to figure out whose things are whose while waiting for their turn in the shower. It could be a comical situation with the characters trying to identify their robes, wands, and other items.
One idea could be a story about the Gryffindor Quidditch team in the locker room before a big match. Maybe there's some friendly banter among the players, like Harry Potter trying to boost the team's morale with a humorous speech. Another could be a story of a new student accidentally stumbling into the Slytherin locker room and the reactions of the Slytherin students.
One idea could be that the scarecrow comes to life and becomes a magical creature that helps Harry Potter in a dangerous task. Maybe it has the ability to sense dark magic and warns Harry of approaching threats.
Perhaps Orochi is a hidden figure in the history of the wizarding world that has been forgotten. Harry discovers some old texts in the Hogwarts library that mention Orochi in relation to a long - lost magical artifact. This leads him and his friends on a quest to find the artifact before it falls into the wrong hands, as it has the power to either control Orochi or be used by Orochi to gain ultimate power over the wizarding world.
One plot idea could be that Harry and Angelina team up for a special Quidditch training session for the younger students. They discover a new flying technique together that gives Gryffindor an edge in future matches. Another could be that they go on a secret mission within Hogwarts to uncover a hidden artifact that has been causing strange magical disturbances. And a third idea is that Angelina gets injured during a match and Harry uses some of his unique magical skills, learned from his various adventures, to help her recover faster than normal.
One idea could be a story where a character has a special power to resist Dementors' effects more than others. Maybe they discover a hidden spell or have a unique magical ability that they use to fight off Dementors when others are in danger. For example, a young witch or wizard who can emit a positive energy that counteracts the Dementors' despair.
One idea could be Norberta getting lost in the Forbidden Forest and Harry has to find her. Another could be Norberta growing ill and Harry, with his knowledge of magical creatures, tries to heal her. Maybe Norberta could get into trouble with some other magical creatures and Harry has to step in to protect her.
In some fanfictions, a great plot twist is that the secret room is not really a secret at all. It was made to seem that way on purpose by Hogwarts founders to test the students' curiosity and courage. So when Harry and his friends finally find it, they realize it was more of an elaborate ruse all along. Also, the room could be filled with magical challenges that are not as they seem at first. For example, a seemingly deadly trap could actually be a test of a different kind of magic, like emotional control or the ability to communicate with magical creatures.