Seiryaku Kekkon demo Koishitai! Horegusuri wo Nondara Konyakusha ga Nikushokukei ni Hyouhen Shimashite

An academic institution welcoming all nobility in the Kingdom of Lilinoa: Lafalle Magic Academy. At this school there are two students of particular interest: Arnold Lirein, the son of a count, and Harley Lashtelle, the daughter of a duke. The two are excelling in school and have known each other for many years... and are in an arranged marriage agreed upon by their families. However, perhaps because of their strong familiarity with one another, the two have never developed a sense of romantic interest. Harley has always felt passionate about the idea of a "happily-ever-after" in marriage, and now with a mission to find a way to get closer to Arnold, she has decided the two could try out a love potion... (Source: MangaPlaza)