One idea could be that Karma gets transported to the Naruto world. He could start off as an unknown entity and gradually get involved in the shinobi battles. Maybe he'd team up with Naruto and use his unique skills from Assassination Classroom to help in missions.
Don't forget about the setting. If the story is mostly in the Naruto world, describe it vividly for readers who may not be as familiar with it. If it's in Karma's world, explain how Naruto adapts. Also, make sure the pacing is right. Don't rush the relationship development between Karma and Naruto, let it build up slowly and naturally over the course of the story.
Strange Tales from a Chinese Studio is an ancient Chinese novel. It tells many fantastic stories, including many plots about karma. In these stories, people could often see the scene of good and evil being rewarded, and the retribution of good and evil was sometimes beyond people's imagination. For example, in the Legend of the White Snake, the White Lady sacrificed everything to save her husband Xu Xian, but in the end, she was punished by the heavens and lost her beauty and life. The power of karma made people feel deep fear and vigilance in the story.
Friendship or the potential for a deeper relationship is another common theme. Some fanfics focus on how they start as just classmates and gradually become closer friends. Others might explore the idea of a romantic relationship budding between them, but always with the backdrop of their distinct personalities and how they have to navigate their differences while getting closer.
I really liked 'Karma and Bakugo: A New Path'. In this fanfic, the author delves deep into how Bakugo's actions in the past come back as karma and how he overcomes it. It has some really interesting plot twists and great interactions between the characters.
Another theme is growth. The idea of karma in these fanfics forces Bakugo to grow as a person. He has to become more empathetic and understanding, which is a big change from his initial brash self. This growth is usually shown through his interactions with other characters, like how he might start to be more collaborative instead of always being competitive.
A great Naruto Karma Mark fanfic is 'Karma Mark: A New Beginning'. In this fanfic, the Karma Mark is not just a power but a key to an entirely new world or dimension. The story could involve the characters traveling through different realms, using the Karma Mark's unique abilities to survive and uncover secrets that were long forgotten in the Naruto universe.
In Naruto fanfics, the Karma Mark often gives characters enhanced physical abilities. For example, they might become faster, stronger, and more durable. It can also grant them unique jutsu or powers that are not part of their normal arsenal. For instance, a character could gain the ability to teleport short distances using the Karma Mark's energy.
Another fanfic called 'Karma, Okuda and the Unexpected Friendship' is also worth checking out. It begins with Karma noticing Okuda's quiet presence in the class and gradually, they form an unlikely friendship. It shows their relationship evolving over time, from simple classmates to friends who truly understand and support each other.