One plotline could be Snape trying to outwit Voldemort in a battle of wits without Voldemort suspecting his true loyalties. It would be full of tense moments as Snape has to be very careful with his every move and word.
A really interesting plotline is when Snape and Hermione are brought together by a time - travel incident. In this scenario, they have to work together to fix the disruption in time, and in the process, they gain a new respect for each other. Also, there are plotlines where Hermione discovers Snape's hidden talents outside of teaching, like his skills in ancient magic or his connection to some long - lost magical artifacts, which leads to an interesting adventure between them.
There might be a fanfiction where Voldemort discovers Snape's true loyalty is not fully with him. This could lead to a really tense showdown between them. Snape would have to use all his skills in magic and deception to survive. Maybe he has to convince Voldemort that he was only pretending to be against him to gain more information for the Dark Lord.
Another plotline could be a time - travel scenario. Imagine Naruko travels back in time and meets a younger Orochimaru. She could try to prevent him from going down the dark path he originally did in the Naruto series. This would involve a lot of character development for both of them, as Naruko tries to understand Orochimaru's motives in the past and change his future. It's a great way to explore their characters without any lemon content.
One possible plotline could be that Snape discovers a hidden vulnerability in Voldemort. Maybe it's related to his Horcruxes. Snape, being the intelligent and resourceful character he is, figures out a way to destroy all of Voldemort's Horcruxes without Voldemort suspecting. Then, he uses his powerful magic skills, perhaps a combination of dark and light magic, to directly confront and kill Voldemort.
One more plotline could be that Haku has a long - lost relative who is in danger, and Naruto helps him to rescue this relative. Along the way, they face a powerful enemy who has a vendetta against Haku's family. They have to use their combined strength and the bonds of their friendship to overcome this enemy and save Haku's relative.
Another interesting plot could be a backstory about how Snape first got involved with Voldemort. Maybe it was out of a thirst for power initially, but then his views changed over time. This could be delved into in great detail, showing his transformation from a potential dark wizard follower to a hero in the fight against Voldemort.
One interesting plotline could be them mentoring a young and troubled student together. They both have different teaching styles and areas of expertise, so seeing them combine their efforts to help a student in need would be fascinating. For instance, Snape with his knowledge of potions and Remus with his understanding of Defense Against the Dark Arts could guide a student who is struggling in both subjects.
One interesting plotline could be that Harry discovers a new, powerful magic that gives him an edge in the fight against Voldemort. For example, he might find a way to combine different spells in an unexpected way. Another could be that Voldemort has a secret weakness that Harry uncovers through his friendships. Maybe one of his friends has a unique connection to an ancient magic that can be used against Voldemort.
One possible plotline could be that the children possess unique magical abilities due to their mixed heritage. For example, they might have the power to control both light and dark magic in a balanced way. Another could be that they are caught in the middle of the two worlds, with the wizarding community being suspicious of them because of their Voldemort connection, while Voldemort's remaining followers might try to use them for their own dark purposes.
Well, in some fanfictions, when Harry surrenders to Voldemort, it leads to a strange alliance. Voldemort, being overconfident, might keep Harry alive thinking he can use him. Harry could then start to learn more about the dark side from within, and perhaps find a way to turn some of Voldemort's followers against him. Also, it could be that the act of surrender causes a shift in the magical balance in the wizarding world. Some ancient prophecies might be set in motion that no one expected, and Harry has to figure out how to use this new situation to his advantage.