Osamu Mikumo is quite popular. His growth as a character in the original series makes him a great focus in fanfiction. He can be written in various scenarios where he overcomes more challenges. Yuuma Kuga is also popular as his unique abilities and his mysterious past offer a lot of room for exploration in fanfiction.
One interesting concept could be alternative character backstories. For example, a fanfiction might explore what led a side character to become an agent. Another concept could be different rankings systems within the Border organization. It could also be about new types of Triggers that are created by the characters in the fanfiction.
If it's a crossover with a Naruto - like ninja world, Naruto himself would be a great addition. His energy and determination could contrast and complement the World Trigger characters. Also, Sasuke with his powerful ninja skills could add an interesting dynamic. In a crossover with a One Piece world, Luffy would be a fun character to include. His carefree yet strong - willed nature would bring a new flavor to the story.
One idea could be a crossover with a magical world. The World Trigger agents suddenly find themselves in a place full of wizards and magic spells. They have to adapt their combat skills to deal with magical creatures and powerful magicians. Another plot could involve a crossover with a post - apocalyptic world. The agents must use their Trigger abilities to survive in a world filled with mutated beasts and scarce resources.
The unique world - building makes 'world trigger novel' interesting. It has a distinct setting with the concept of the Neighbors and the Trigger system.
The 'world trigger visual novel' probably delves deeper into the backstories of the characters in the World Trigger universe. For example, it might explore how the agents of Border came to be, their training, and their personal struggles. It could also provide more details about the Neighbors, their culture, and their motives for invading Earth. It offers fans a chance to experience the story from a different perspective, with different narrative choices and paths.