Well, one plotline could be Sirius getting into an argument with another character and saying 'and shut up' in a moment of anger. Maybe it's with Snape and it leads to a whole confrontation that reveals some long - hidden secrets between them.
There are so many Sirius Black fanfictions out there. To find ones with that specific phrase, you might need to do a more in - depth search. Maybe check some Sirius Black - centric fanfiction communities. They often have members who are really into finding unique fics. They could point you in the right direction to find a story with 'and shut up' in it.
One interesting plotline could be Sirius teaching Harry advanced magic in secret. For example, Sirius might show Harry how to perform Patronus charms earlier than he does in the original story. This would give Harry an edge in dealing with Dementors and other dark creatures.
Some fanfictions explore a scenario where Marlene survives the war and she and Sirius get a chance to rekindle their relationship. It delves into how they deal with the trauma of the war and their past feelings for each other. They might have to face the judgment of the wizarding society which has changed after the war. This plotline can be very emotional and complex as it involves a lot of character development and exploration of post - war wizarding world.
One common plotline is Sirius Black escaping from Azkaban earlier and secretly training Harry in advanced magic. Another could be Sirius and Harry going on a hidden adventure to uncover more about Harry's parents. There are also stories where Sirius plays a more active role in the fight against Voldemort at Hogwarts, using his knowledge of the Dark Arts and his Animagus form to their advantage.
In some 'sirius black after azkaban fanfiction', there could be a plotline where Sirius has to deal with the stigma of being an escaped convict, even though he was wrongly imprisoned. He might face distrust from some in the wizarding community. At the same time, he could be on a journey to find out who really betrayed his friends all those years ago, which leads him on an adventure full of mystery and danger.
One possible plotline could be Sirius taking control of a difficult situation within the wizarding world, like dealing with dark wizards. Maybe he uses his skills and knowledge to outwit them.
One interesting plotline could be how Sirius helps Harry discover more about his parents in a more personal way. Since Sirius was James Potter's best friend, he could share countless stories and memories that Harry never knew. Another plotline might involve Sirius teaching Harry some advanced magic that he wouldn't learn at Hogwarts. This could give Harry an edge in dealing with the various threats he faces. Also, their relationship could be explored in depth, showing how Sirius becomes not just a guardian but also a true father figure to Harry.
One interesting plotline could be Narcissa and Sirius having to team up against a common enemy in the wizarding world. Maybe there's a dark force threatening both the Black family's reputation and Sirius's fight for justice. They start off distrusting each other but gradually learn to work together.
One interesting plotline could be a mystery - solving one. Harry discovers some strange artifacts in Grimmauld Place that were left by Regulus. With Sirius (if he's alive in the fic), they try to figure out what these artifacts mean and it leads them to uncover a long - forgotten plot by Voldemort. Another plotline could be a redemption arc for Regulus. Harry, after learning about Regulus's attempts to undermine Voldemort, tries to clear his name in the wizarding world, which causes some friction with those who still see the Black family as mostly dark wizards. And there could be a plotline about family secrets. Sirius and Harry find out that there are hidden magical abilities in the Black family bloodline that only Regulus knew about, and they have to figure out how to use or control them.
One possible plotline could be Harry learning more about his parents from Sirius. Sirius could share all the little details, like how James was in school, his mischievous deeds, and how he courted Lily. This would give Harry a deeper connection to his family's past. Another could be Harry and Sirius training together in magic, especially in defensive spells. Sirius, being a skilled wizard, could teach Harry some unique spells and techniques that he might not learn at Hogwarts. Also, they could have adventures in the wizarding world together, exploring places that are off - limits to most students.