They usually have a growth arc, even if they start out OP. Take some of the MCs in light novels like 'Log Horizon'. Shiroe, while already having strong gaming knowledge and skills, still grows in terms of his leadership and understanding of the new world he is in. This growth makes them more relatable and interesting, despite their overpowered nature.
One characteristic is their unique abilities. For example, in 'Overlord', the MC has abilities that are far beyond normal characters in the game - turned - real - world setting. Another is their rapid growth or high starting level. In 'Sword Art Online', Kirito starts with a good level of skills which he further hones.
They usually have a strong sense of justice or a unique goal. Take Luffy from 'One Piece' (which also has light novel adaptations). His goal of becoming the Pirate King drives him forward, and his rubber powers along with his unwavering will make him overpowered in his own way. He stands up against strong enemies to protect his friends and achieve his dream.
Often, an OP female MC has extraordinary combat skills. For example, like Saber in 'Fate/Zero' and its related works. She can wield her sword with great proficiency and take on multiple foes at once.
Typically, an OP MC in fantasy light novels has extraordinary powers or skills. For example, they might be a master of magic like in 'Overlord', where Momonga has a vast array of powerful spells. They also often have a high level of intelligence, which helps them strategize and outwit their opponents. In 'Sword Art Online', Kirito uses his knowledge of the game mechanics to his advantage. Another characteristic is quick adaptation. In 'That Time I Got Reincarnated as a Slime', Rimuru adapts to his new form and surroundings very fast and uses it to gain power.
I think 'That Time I Got Reincarnated as a Slime' is also a top OP MC light novel. Rimuru Tempest, the slime, gains many powers and abilities as he progresses. He starts from being a weak slime but quickly becomes very powerful, with skills like 'Predator' which allows him to absorb other beings and gain their powers. It's really interesting to see how he uses his OP abilities to build his own nation.
The genre also often features elements of self - discovery for the MC. Despite being overpowered, they still need to figure out their place in this new world. They may face moral dilemmas, form relationships, and learn about the history and secrets of the isekai world. This combination of OP abilities and personal growth in a new and strange setting is what makes the 'op mc isekai light novel' genre so appealing to many readers.
One great OP MC (Overpowered Main Character) fantasy light novel is 'Sword Art Online'. The main character, Kirito, is extremely skilled and powerful in the virtual world of Aincrad. Another is 'Overlord'. Momonga, the main character, is a very powerful magic caster in a game world that has become a reality. Also, 'That Time I Got Reincarnated as a Slime' is good. Rimuru starts as a slime but quickly gains incredible powers and builds his own nation.
In light novels, 'op mc from start' often refers to an overpowered main character right from the beginning. This means the character has abilities, skills, or knowledge that are far superior to others at the start of the story, which can lead to some really interesting plot developments as they either face challenges despite their power or use it to quickly rise in their fictional world.
Typically, they are often very powerful from the get - go. For example, in 'Overlord', the main character has a vast array of powerful spells and an army at his disposal right after being transported to the new world. This immediate power gives them an edge in the new and often dangerous isekai settings.
One such light novel could be 'Sword Art Online'. The main character Kirito is extremely powerful and often overcomes difficult challenges with ease.