Who could be the main antagonist in a 'naruto x natsumi x kushina fanfiction'?

One possible plot could be that Natsumi is a new character who befriends Naruto. Through Naruto, she gets to know about Kushina. They then form a unique bond where they all support each other in Naruto's journey to become Hokage. Natsumi might have some special skills that complement Naruto's and Kushina's abilities.

It could be an old enemy of Kushina's who was thought to be dead but has now returned. Maybe someone from her days in the Uzumaki clan who has a vendetta against her and now sees Naruto as an obstacle too.

It could be a rogue ninja from a forgotten clan who wants to steal the unique powers of Naruto, Naruko, and Satsuki. He sees their combined potential as a threat to his own evil plans of taking over the ninja world. This antagonist might have some ancient and powerful jutsu that the three heroes have to figure out how to counter.

It could be a powerful dark wizard from the Enchantress' world who follows her to the Naruto universe. He wants to capture the Enchantress and use her powers for his evil plans, and also sees the chakra in Naruto's world as a new source of power to conquer. He could have dark magic that can nullify ninjutsu, creating a real challenge for Naruto and the Enchantress.

Perhaps a powerful demon that has a grudge against the power of Amaterasu. It targets Naruto because he is the one who seems to be getting closer to Amaterasu. The demon could be from an ancient time when Amaterasu was first used to seal it away, and now it's back to stop Naruto from fully understanding and using Amaterasu.

Kawaki could also be a potential antagonist. If he feels that Delta's connection with Naruto is a threat to his own place in Konoha or his relationship with Naruto, he might act against them. He has a complex past and his insecurities could drive him to oppose their alliance.

Mephisto could also be a great main antagonist. His ability to corrupt and manipulate could pose a real threat to Naruto. Mephisto might try to turn Naruto's friends against him or corrupt Naruto himself. Since Naruto values his comrades highly, this would be a difficult situation for him to deal with. And if Mephisto manages to get into Naruto's head, it could lead to some really intense and dark moments in the fanfiction.

It could be a rogue ninja from a long - forgotten clan. This ninja might see the growing relationship between Naruto and Sara as a threat to his own plans for power. He could try to disrupt their villages' alliance and target them specifically.

It could be another Predator. Maybe a rogue Predator that doesn't follow the code of its kind. This rogue Predator might see Naruto and his friends as a threat to its own plans in the Naruto world and tries to eliminate them. It could also use its advanced technology against them in cruel ways, making it a formidable antagonist.

It could also be Madara Uchiha, especially if the fanfiction involves time - travel or alternate timelines. Madara has his own plans for the Uchiha clan and the world, and he might not want Naruto interfering with his grand scheme while also being wary of Fugaku's actions.