I have no idea what is the main plot of the story but it feels like two horny person trying to kiss or consummate their relationship with a lot of distractions for comedic value. There is also the a lot of non stop misunderstanding for comedic value and the ML flip flop to Locked the FL up to Doki Doki as sweet. The ML goal is to keep the FL while the FL goal is have more intimacy which makes the ML sister appearance feel like a random plot and the mystery of FL soul from the magician like an random afterthought insert to make suspense to only be forgotten and later add in our of nowhere
Instead the manhwa I mistook "The Grand Duke is Mine" is much more interesting than this despite the similar cover of a black hair ML and blond hair FL with a duke in the title.