Another theme is the idea of the outsider. Naruto has always been an outsider in his own world to some extent, and Samus is often alone in the vast Metroid universe. When they meet in crossover fanfictions, this sense of being an outsider is explored further. They have to learn to trust each other and work together despite coming from such different backgrounds.
Power - up and evolution is also a common theme. In the Metroid series, Samus has different power - ups and her suit evolves. In Naruto, the characters grow in power through training and new jutsu. In crossovers, often Naruto will experience something like a power - up similar to Samus' suit upgrades, or Samus might learn about the concept of chakra and use it in a new way, which ties into this theme of power - up and evolution.
Survival in a new environment is another theme. Naruto characters suddenly in the Metroid universe, or vice versa, have to figure out how to survive. They need to adapt to new threats, whether it's the space pirates in Metroid or the powerful shinobi in Naruto. This theme adds a lot of excitement and adventure to the fanfictions.
One main theme is adaptation. Naruto has to adapt to the new rules and environments of the Metroid universe.
In 'Metroid male oc fanfiction', the theme of power and its implications is quite common. The male oc might gain new powers or struggle with the power he already has. This could lead to internal conflicts as he decides how to use his power. Another theme is loyalty. He could be loyal to a certain faction or character, or he might face situations where his loyalty is tested. And of course, the overarching theme of the fight against the Metroid - related threats is always present, whether it's the Metroids themselves or other villains in the series.
Friendship is a very common theme. Since it's about Naruto and his friends in a crossover, it often shows how their bonds are strengthened or tested in the new situations. For example, they might have to rely on each other more than ever.
A common theme is the clash of cultures. Naruto's ninja culture from his world is very different from the military - and magic - based culture in 'The Gate'. So, exploring how these two cultures interact is often seen. For example, Naruto might introduce the concept of chakra to the people of 'The Gate' world.
Character growth is also a major theme. In a long 'Naruto' crossover fanfiction, Naruto usually has to face new challenges in the crossed - over world. This forces him to adapt and grow in ways he didn't in his original 'Naruto' world. For instance, in a crossover with the 'Fullmetal Alchemist' world, he has to learn about alchemy and its rules, which broadens his understanding and skills.
One common theme is power. The shinju is a powerful entity, and when crossed over with Naruto, it often involves the characters either seeking its power or having to deal with the consequences of its power. For example, in many fics, Naruto might be tempted by the shinju's power to achieve his goals more quickly.
A common theme is the clash and then the fusion of different power systems. Naruto's chakra - based ninja skills and the magic from the other universe, like spells in Harry Potter or magic in Fairy Tail, often start by being at odds but then find a way to work together.
A major theme in these fanfictions is identity struggle. Naruto, being in a chaotic crossover, may question who he is and how he fits into this new, disordered world. Also, the theme of friendship and alliances is quite common. He has to form new alliances with characters from the chaotic world, and these relationships are explored in depth. For instance, he might team up with a chaotic being who has different motives, and they have to work together despite their differences.
One common theme is redemption. Naruto, being banished, often has to prove himself all over again in the new crossovers, seeking redemption for whatever led to his banishment in the first place.