Another plotline could be that Magnus' uncle is looking for something specific and alwc has a clue or an item that Magnus' uncle needs. So, Magnus' uncle has to convince alwc to give it up or help him. Along the way, they face various challenges, both from external forces and from their own differences in personality and beliefs. This could lead to a lot of character development for both of them and an interesting story arc.
I'm not sure which specific 'alwc meets magnus uncle fanfiction' is available. You could try searching on popular fanfiction websites like Archive of Our Own (AO3) or FanFiction.net.
In the 'alec meets magnus uncle fanfiction', it could be that Magnus' uncle has some interesting stories about Magnus' past that he shares with Alec. This could help Alec understand Magnus better. For example, he could learn about Magnus' early days as a warlock and the challenges he faced. It might also be a situation where Alec's Shadowhunter background causes some initial tension, but then they find common ground through their love for Magnus.
A really cool plotline could be a time - travel scenario within the fanfiction. Magnus Chase and the Seven get sent back in time to a crucial moment in Norse mythology. They have to make sure the events play out correctly without changing history too much, while also finding a way to bring something back from that time period to help them in their present - day struggles against their enemies.
Another plotline might be that in a world where the laws of nature are different for certain characters, Magnus and Alec decide to have a child in this unique way. The story could then focus on how they deal with the reactions of their friends and family, and also the challenges of Alec's pregnancy, like his changing body and emotions. It could also involve them preparing for the arrival of the baby, from choosing a name to setting up a nursery.
One possible plotline could be that Magnus Bane kidnaps someone in order to protect them from a greater danger. Maybe there's a powerful dark magic user after a young warlock, and Magnus takes the warlock to a hidden location. Another could be that Magnus is misjudged, and he actually didn't kidnap but was trying to rescue someone who was in a magically - induced coma and had to move them quickly. A third plotline might be that Magnus kidnaps someone as part of a deal with a demon, but then has a change of heart and tries to find a way out of the deal while keeping the kidnapped person safe.
It could be another warlock who doesn't like the idea of Alec, a Shadowhunter, getting involved with Magnus and his family.
There could also be a plotline where there is some sort of danger threatening the Pride Lands. Kovu and Mufasa, despite their differences, team up to face this threat. Kovu brings his unique skills and knowledge from his pride, and Mufasa uses his wisdom and leadership. As they work together, they develop a mutual respect for each other that was not there before.
Maybe Talion could help Frodo on his journey to destroy the One Ring. He has his own combat skills, so he could offer protection against the various threats that Frodo faces.
One possible plotline could be a competition between Naruto and Sebastian. For example, a contest of skills where Naruto shows off his ninja moves and Sebastian displays his butler feats.
A possible plotline could be that Yugito is kidnapped by an enemy organization. Naruto hears about it and decides to rescue her. Along the way, he discovers more about Yugito's past and the importance of the Two - Tails to the Hidden Cloud. Another plotline might be that they both enter a mysterious ninja tournament. There, they have to fight side by side against powerful opponents and learn to trust each other's skills.