It could be a more action - packed story. The soldier could be from a world at war, and when he meets the My Little Pony characters, he discovers that their world is also facing some kind of danger. He then teams up with the ponies, using his combat training and the ponies' unique magical abilities to fight off the common enemy. This could be a story about how different strengths can be combined to overcome difficulties.
The soldier might be a bit rough around the edges at first. He could be used to a more serious and tough environment. But the ponies, with their friendly and kind nature, would probably try to make him feel welcome. For example, Twilight Sparkle might offer to show him the library and share knowledge, while Pinkie Pie would throw a party to cheer him up.
One possibility is that Deadpool is on a mission in his own universe and there's a portal malfunction which sends him to the My Little Pony realm. There, he might meet Twilight Sparkle who is intrigued by this strange new being. Deadpool could try to teach the ponies some of his combat moves in a really goofy way, while the ponies introduce him to their magic and harmony. This could lead to a story where they team up to face a common threat, like an evil force that wants to disrupt the peace in both their worlds.
One possible plot could be that Naruto somehow gets transported to the My Little Pony world. He might initially be confused by the colorful and peaceful land, but then he could use his ninja skills to help the ponies when they face a threat, like a powerful dark magic user. He could teach the ponies some of his combat moves, and in return, learn about the magic of friendship from them.
One possible plot could be that Spongebob and Patrick get lost in a magical portal and end up in Equestria from My Little Pony. They meet Twilight Sparkle and her friends. Spongebob's positive attitude and Patrick's goofy nature could create some humorous situations as they try to figure out how to get back home while also getting involved in the local pony adventures, like helping to solve a problem with a magic spell gone wrong.
In a 'pokemon meets my little pony fanfiction', a great plot could be that there's a dark force threatening both the Pokemon and My Little Pony universes. A group of strong Pokemon like Charizard and a team of brave ponies including Rainbow Dash join forces. They travel through different regions of both worlds, gathering allies and learning new skills from each other to defeat this common enemy. It would be full of action, friendship, and discovery.
Well, a lot of things could happen. Maybe the human gets transported into the My Little Pony world. They could befriend the ponies and have all sorts of adventures, like helping them solve a problem in Ponyville. Or perhaps the ponies come to the human world and they all have to figure out how to get along in a very different environment.
Another theme could be sacrifice. Some pony soldiers may have to make sacrifices for the greater good of Equestria. This could be sacrificing their own time, resources, or in extreme cases, their lives. It adds a more serious and heroic tone to the fanfictions.
There could be a plot where Sonic accidentally ends up in Equestria. At first, the ponies might be a bit confused by this strange, speedy blue creature. But then they realize his good heart and his skills. Together, they could go on quests to discover new places in Equestria that are hidden or lost, using Sonic's speed and the ponies' unique abilities.
Perhaps the soldier puppy could be a messenger in a story involving My Little Pony. The ponies are often into magical and important tasks, and the puppy, with its trained abilities, could carry messages between different pony groups or to other lands. Also, the pony might teach the puppy some of its magical ways in return for the puppy's services.
One possible plot for this fanfic is that a group of ponies accidentally stumbles upon a Star Wars spaceship. They end up on board and start exploring. The Star Wars crew is initially shocked by these strange, colorful, and small equine - like creatures. But as time goes on, they notice the ponies' strong sense of friendship and loyalty. The ponies, in turn, are fascinated by the technology on the ship. They might even help the Star Wars characters solve a problem using their unique pony abilities.