One factor is the sense of wish - fulfillment. Readers like to imagine themselves in the shoes of a character who can easily overcome challenges. For example, in 'That Time I Got Reincarnated as a Slime', Rimuru's ability to gain new powers so effortlessly is exciting. Another aspect is the ability to change the world around them. An overpowered MC like Momonga in 'Overlord' can reshape the new isekai world according to his will, which is very appealing.
A really good overpowered MC isekai novel is 'The Rising of the Shield Hero'. Naofumi is initially treated unfairly but as he progresses, he becomes extremely powerful. His shield gives him unique abilities that set him apart from others in the isekai world. Then there's 'Log Horizon'. Shiroe, the main character, has a great intellect which, combined with his in - game skills, makes him overpowered in the world he's isekaied into. Also, 'Konosuba' has an interesting take on an overpowered MC. Kazuma has some unique abilities, and his party members also contribute to his overall 'overpowered' situation in the comical isekai world.
Another aspect is prior knowledge or experience. In some light novels, the MC is reincarnated or transferred from another world. Like in 'Konosuba', Kazuma has knowledge from his previous life which he uses to his advantage in the new world, and this knowledge combined with his unique skills makes him overpowered in certain situations.
Some popular overpowered MC (main character) novels include 'Solo Leveling'. In this novel, the MC starts off weak but gradually becomes extremely powerful with unique abilities. Another one could be 'Overlord', where the MC is an incredibly strong character in a game - like world. And 'The Legendary Mechanic' also features a very overpowered MC with great skills and development in a sci - fi setting.
The harem aspect means there are multiple female characters who are attracted to the MC. In these manga, the relationships can range from simple admiration to deeper emotional bonds. The female characters often have diverse personalities and abilities, adding to the complexity of the story. For instance, in 'Death March to the Parallel World Rhapsody', the harem members include a princess, an elf, etc.
One popular one is 'Overlord'. The main character Momonga is extremely overpowered. He starts as a max - level player in a game and when the game world turns into a real one, his abilities are far beyond others. His magic powers and strategic mind make him nearly unbeatable.
Often, there is also a sense of the protagonist being an outsider who has to navigate this new world. They might face initial distrust from the natives but gradually prove themselves. In terms of power, there are often power - leveling or power - up sequences where the protagonist gets even stronger over time. For instance, in 'The Rising of the Shield Hero', the main character starts with a somewhat limited power but gradually becomes very powerful through his own efforts and new abilities he acquires.
To write an overpowered mc fanfiction, start with a strong concept for the character's power. It could be something as simple as being able to fly at supersonic speeds or as complex as having the ability to rewrite reality. Then, build a cast of supporting characters around the mc. These characters can react to the mc's power in different ways, some in awe, some in fear. The story should also have a goal for the mc, whether it's to save the world, find a lost family member, or just to find a place where they can belong despite their power.
One popular overpowered mc fanfiction could be those where the main character has god - like powers from the start. For example, in some stories, the mc can manipulate time and space effortlessly. Another type might be where the mc has an unbeatable skill set that allows them to defeat any opponent with ease, like having super strength and lightning - fast reflexes combined.
The theme of leadership also appears frequently. In 'The Rising of the Shield Hero', Naofumi has to lead his small group of allies against much larger forces. His overpowered abilities give him the means to do so, but he also has to develop leadership skills. Also, there is often a theme of justice. These overpowered characters usually end up fighting for what they believe is right. They use their power to protect the weak or to right the wrongs in the world they inhabit, whether it's a virtual world like in 'Sword Art Online' or a more traditional fantasy world like in other novels.