Well, for a Mafia Nanny fanfic, a great plot could be that the nanny is hired to look after the mafia family's youngest member who is being targeted by a rival mafia group. The nanny then has to use her wits and some unexpected skills (like martial arts or hacking) to protect the child. Or perhaps the nanny is actually an undercover agent sent to gather information on the mafia family, but she starts to have second thoughts as she bonds with the family, especially the child. Also, it could be that the mafia family is in the middle of a power struggle, and the nanny gets caught in the middle, having to choose which side to support to ensure the safety of the child she cares for.
One idea could be that the nanny has a mysterious past related to the mafia world herself. Maybe she was once involved in a rival gang and is now trying to start a new life as a nanny, but her past catches up with her when the mafia family she works for discovers her true identity. Another plot could be the nanny accidentally overhears some crucial mafia business and has to decide whether to keep quiet or use it to her advantage. And a third idea is that the mafia boss's child becomes very attached to the nanny, and the boss has to deal with his own feelings for the nanny while also protecting his family's secrets.
In a Mafia Nanny fanfic, a plot might involve the nanny being a long - lost relative of the mafia family. She doesn't know about this connection when she's hired, but as she works there, she starts to notice some strange similarities and family traits. Meanwhile, there could be a threat from outside the family, like a group of assassins. The nanny, with her natural maternal instincts, decides to fight for the safety of the family she has come to care about. Another idea is that the nanny is a reformed criminal herself and she tries to steer the young members of the mafia family away from a life of crime by telling them her own stories of regret and redemption. Also, the relationship between the nanny and the mafia boss could develop into a romantic one, but they face many obstacles due to their different worlds.
One idea could be to cross it with another game like Grand Theft Auto. The protagonist from Mafia 3 could find himself in the chaotic world of GTA, dealing with different gangs and their unique styles. He might have to adapt to the new city layout and rules.
Perhaps the mafia is involved in a plot to steal ancient ninja artifacts that hold great power. Naruto and Sakura are assigned to protect these artifacts but end up having to infiltrate the mafia to find out who's behind the plan. Along the way, they face challenges like betrayal from within the mafia ranks that they thought they could trust, and they have to rely on each other's skills and their bond as teammates to succeed.
One idea could be that Percy discovers a secret mafia within the demigod world that is controlling the distribution of magical artifacts for their own gain. He has to go undercover to expose them.
One idea could be a mafia family in the Highschool DxD universe trying to recruit Issei for his unique abilities. They see his potential as a valuable asset in their underworld operations.
One idea could be an OC who has a special talent for music. The OC could use music to soothe the unruly children in the story, much like Nanny McPhee uses her magic. For example, when the children are about to have a big fight, the OC plays a soft melody on a flute and they all calm down.
One plot idea could be that the mafia boss is secretly protecting Hogwarts from a new dark threat. He uses his underworld connections to gather information that the Ministry of Magic can't access. For example, he might discover a group planning to steal powerful magical artifacts from the school. Another idea is that the mafia boss is actually a wizard who was exiled from the wizarding world long ago and has built his own criminal empire in the Muggle world. But when he hears about Voldemort's return, he decides to use his resources to help Harry Potter, in his own unorthodox way. A third idea could be that the mafia boss has a vendetta against a Death Eater who once wronged him in the past, and he teams up with Harry and his friends to take the Death Eater down.
The mafia king could be a new threat that emerges after Voldemort's defeat. He sees the power vacuum in the wizarding world and decides to take over. Harry, being the hero, has to gather his old friends and some new allies to face this new menace. The fanfiction could explore how the wizarding world has changed after the big war and how it copes with this new type of threat.
One plot idea could be that Sasuke and Naruto are part of rival mafia families. They are initially enemies but gradually find common ground as they uncover a greater conspiracy that threatens both their families. For example, a third, more powerful mafia group is trying to take over their territories.
You might like 'Underworld Guardians'. It has a similar mafia backdrop and focuses on characters with complex loyalties. The storylines are engaging and full of suspense.
One interesting mafia fanfic could be about a young detective who infiltrates a mafia family. There's this whole drama of her trying to hide her identity while falling in love with one of the mafia members. It's full of suspense and romance.