The best 18+ romantic storylines ditch the perfect male lead. Instead, you get:

South Korea's rigid social hierarchy (age, job title, school rank) is erotic dynamite. The best 18+ Korean IS weaponize this.

If you wish to expand this draft, you could include:

To understand the romance in an 18+ Korean IS, you must first understand the social reality it mirrors. South Korea has one of the lowest marriage rates in the OECD and a complex dating culture where the line between "dating" and "exclusive relationship" is heavily ritualized.