Another possibility is that it focuses on the technological future of the Arcane universe. The story could be about how new inventions in Piltover are going to change the relationship between the two cities. There could be a scientist character who watches the future of technology and tries to either encourage or prevent certain advancements based on what they see.
Vi could be the main character. She's strong - willed and has a connection to both Piltover and Zaun. In a future - watching scenario, she could use the knowledge to protect those she loves and bring about peace between the two areas.
Perhaps the Marauders watch the future and are shocked to find out that some of their group won't survive the upcoming wizarding wars. They might then start to take extra precautions and train harder to change that future. They could also see new friendships and alliances being formed in the future that they then try to encourage in their own time.
The main plot might center around a mystery that the ASL group stumbles upon in this future setting. It could involve a missing piece of technology or a person who holds the key to a new world order. They then have to navigate through a complex web of clues and face various antagonists who don't want them to uncover the truth. This would involve a lot of action, some tense moments of near - discovery and setbacks as they slowly piece together what's really going on.
Maybe in the fanfiction, the story focuses on a character from the future coming back to the present in 'Jujutsu Kaisen Watch the Future'. This character has knowledge of future events that could either save or destroy the current world of Jujutsu sorcerers. The main characters then have to decide whether to trust this person and how to use the information without causing chaos.
One possible plot could be that the characters face a new, more powerful type of Grimm that has abilities they've never seen before. They have to quickly adapt and find new ways to fight. Maybe Ruby discovers a new form of her scythe's power to combat this threat.
In 'naruto in the future fanfiction', perhaps Naruto has passed on his ninja way to a new generation. His son or disciple could be facing a new threat that combines old and new jutsu. Maybe they have to deal with a group that has found a way to use ancient, dark jutsu in a modern, technological world.
Well, it could be about a world where technology has advanced to the point that humans can teleport at will. The main character, a young scientist, discovers a flaw in this system that could lead to the destruction of the universe. So, he embarks on a journey to fix it.
Well, it could be about Ladybug and Chat Noir finally revealing their identities to each other and having to deal with the consequences. Maybe they face a new, more powerful villain that is a threat to all of Paris and they have to use their combined powers in new ways.
One possible plot could be that Percy discovers a magical device that sends him to the future. There, he might find a world that has been drastically changed by the actions of the gods in his time. Maybe the demigod camps have evolved into something completely different, and he has to adapt to new rules and powers.
In this fanfiction, it could be that the future has a new Dark Lord. The Marauders are brought forward in time to stop this new threat. They face challenges like understanding the new forms of magic and technology that the future Dark Lord has harnessed. They also have to deal with the fact that the future wizarding world has different social and political structures. They might start by infiltrating the Dark Lord's lair using their Marauder's Map - like skills, but find that the map doesn't work as well in the future, leading to all sorts of interesting and dangerous situations.