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.
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.
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.
One great light novel with a powerful main character (MC) is 'Overlord'. The MC, Ainz Ooal Gown, is extremely OP (overpowered). He starts as a max - level character in a game world that has suddenly become a reality. His abilities and strategic mind make him nearly unbeatable.
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.
The light novel 'Akame ga Kill!' also has an OP female MC in Akame. She is a highly trained assassin with a powerful teigu (a special weapon). Her skills in combat and stealth are top - notch, allowing her to take on much stronger opponents.
One great anime is 'Sword Art Online'. The main character, Kirito, is extremely overpowered (OP). He is highly skilled in the virtual reality world of SAO. In the series, he also has a love story with Asuna. Their relationship develops as they face various challenges together in the dangerous game world.
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.