Perhaps the Dark Puppeteer creates illusions based on Kushina to trick Naruto. Naruto, being strong - willed, has to break through these illusions by delving deeper into his memories of his mother. He could then use the love and strength he got from Kushina to defeat the Dark Puppeteer.
Perhaps they are living in a parallel universe where everything is dark and gloomy. Dark Naruto and Dark Kushina could be trying to find a way to break through to the normal universe. They might encounter strange versions of their friends and foes, and have to battle their own inner demons along the way. For example, Dark Naruto might struggle with the darker aspects of the Nine - Tails' power that he has fully embraced in this universe.
One interesting plot could be that 'dark kushina' initially tries to manipulate Naruto for her own goals but gradually develops real feelings for him as she gets to know him better. Another could be that they are forced to work together to save the Hidden Leaf Village from a powerful enemy.
She could also be developed in relation to the Dark Puppeteer's backstory. Maybe there was a past encounter between them that was never fully resolved. This would add depth to her character as Naruto uncovers more about her past and how it relates to the current threat.
A third plot idea is a crossover where Kushina enters a world that combines Naruto elements with elements from a post - apocalyptic setting. She has to use her ninja skills to survive in this harsh new world. Maybe there are new types of chakra - based threats or she has to find a way to restore order using her leadership skills. This would put her in a completely different situation compared to what she's used to in the normal Naruto world and force her to adapt and grow in new ways.
One idea could be exploring Kushina's life before Naruto was born in more detail. Maybe show her training as a jinchuriki and how she met Minato. Another could be a story where Naruto discovers a hidden journal of Kushina's that reveals family secrets and advice for him.
Well, perhaps Demon Naruto has some sort of special connection to Kushina that is related to his demonic powers. For example, her Uzumaki bloodline might be the key to controlling or understanding his demonic side better. And they could go on a journey to discover the secrets of his powers together.
Another plot could be a 'what - if' scenario. What if Kushina didn't die? Naruto grows up with his mother around. The story could explore how Kushina helps Naruto train, not just in ninjutsu but also in understanding his Uzumaki heritage. It could also show how their relationship affects Naruto's relationships with others in the village, like how he might be more confident with Kushina's support.
Well, a really interesting plot could be a fanfiction where Mikoto and Kushina's spirits are somehow able to communicate with Naruto at crucial moments in his life. They give him advice and strength, even though they are no longer alive. Also, a story about how they worked together to try and bridge the gap between the Uchiha and the rest of the village would be fascinating. They could use their influence and relationships to bring about positive change. This would involve a lot of character development for both of them and would show their importance in the Naruto world beyond just being Naruto's mother and a friend's mother.
One idea could be that the evil Naruto tries to manipulate Kushina's power for his own dark purposes. Maybe he wants to take over the Hidden Leaf Village using her influence as his mother. Another could be that he forms an alliance with the village's enemies, and Kushina has to make the tough choice between stopping her son or trying to save him from his evil ways.
One idea could be exploring Kushina's life before Naruto was born in more detail. Maybe show her training as a Jinchuriki and how she met Minato. Another could be a story where Naruto gets to time - travel and meets his mother when she was his age. It would be a great chance to see their relationship develop in a different way.