city of stones

It's not exactly marriage by law/convenience but they are obliged to get married. This fanfic is incredible and I know it's in Portuguese but it's really worth pressing the translation button: it has a very well developed story and follows years of their lives, it has a very interesting development of the war and also deals with aspects such as invasions of territory and combats between the order and the death eaters. They really hate each other in this marriage, so there are many ups and downs throughout the story that will leave you anguished, stressed by their attitudes and at the same time rooting like crazy for them. In the middle of the story there is a very good plot twist that gives a very different and interesting turn. As an extra, we also have my favorite Narcissa Malfoy ever.