Hmmmmm. Royal/war au, basically 2 kingdoms are at war and the main generals some how accidentally falls in love. 2, Highschool au where the mc (or shipped character) meets the other through a school festival (between 2 schools), fall in love and distant relationship. Another one, (but more cliche and angst), lovers are recarnated and only one person knows their past life, meets the other, tries falling in love again but other drifts away.
Ok thats a lot of ideas- you can use any, just give a teenise little credit. Hope ya make a book
