Isekai manhwa refers to Korean comics where characters find themselves in otherworldly or parallel dimensions. It's a popular genre that offers exciting and imaginative storylines. Sometimes the characters gain special powers or have to overcome various challenges in these strange new worlds.
One great completed isekai romance novel is 'My Next Life as a Villainess: All Routes Lead to Doom!'. It tells the story of a girl who is reincarnated into the world of an otome game as the villainess. She tries to change her fate and in the process, falls in love. Another is 'Ascendance of a Bookworm', which also has elements of isekai and a budding romance as the main character tries to create books in a new world she's been reborn into. And 'That Time I Got Reincarnated as a Slime' has some romantic undertones in the midst of its isekai adventure as Rimuru builds his new world and forms relationships with various characters.
The combination of isekai and romance allows for a lot of creative plotlines. In completed novels like 'The Saint's Magic Power is Omnipotent', the isekai element gives the opportunity for the heroine to discover new powers and a new self, which in turn affects her romantic relationships. Also, the exploration of different cultures in the isekai world can add depth to the romance. For instance, in 'Knight's & Magic', the new world has its own set of values and traditions that influence how the characters interact romantically.