Another common theme is the fish - out - of - water situation. The MC is transported to a new world, so they have to adapt to new cultures, magic systems, and social structures. In 'Konosuba', Kazuma has to deal with all the crazy things in the isekai world while trying to make the best of his situation with his OP party members. And they often have a goal, like saving the new world or finding a way back home, which drives the story forward.
Sure. 'Overlord' is a great isekai novel with an OP main character. Momonga, the protagonist, gets transported to another world and has incredible power from the start. Another one is 'That Time I Got Reincarnated as a Slime'. Rimuru starts off as a slime but quickly becomes very powerful in the new world.
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.
Well, one common theme is the exploration of the isekai world itself. The OP characters often go on adventures, discover new places, and uncover secrets. Another is the concept of relationships. They form alliances, make friends, and sometimes enemies in the new world, and these relationships are shaped by their OP status. Also, the theme of challenging the status quo is present. Their OP abilities give them the power to change things in the world they are transported to, whether it's the political system or the way magic is used.
Power progression is a common theme. The OP main character usually starts from a certain level of strength and becomes even more powerful over time. Another is the development of relationships with multiple female characters. They often start with misunderstandings or the main character helping the females in some way, and then relationships grow.
One popular isekai op novel is 'Overlord'. In this novel, the main character is transported to a different world with extremely powerful abilities. He has to navigate this new world while being almost overpowered compared to the native inhabitants. Another great one is 'Tensei Shitara Slime Datta Ken'. The protagonist, reincarnated as a slime, quickly gains OP (overpowered) abilities and builds his own nation in the isekai world. There's also 'No Game No Life' where the siblings are transported to a world ruled by games and they possess incredible skills and intelligence that make them OP in this new realm.
Sure. 'Date A Live' is a great 'op mc harem light novel'. Shido Itsuka has the ability to seal the powers of the Spirits, which are powerful female entities. He ends up in a harem - like situation as he tries to save the Spirits. Also, 'High School DxD' features Issei Hyoudou, an OP main character who is surrounded by a bevy of beautiful female devils and angels, making it a typical harem light novel.