Well, in such a fanfiction, their married life might be a blend of chaos and harmony. Esdeath's love for Tatsumi is intense. They could be living in a world where they face challenges from both the outside, like enemies who oppose their union, and the inside, like their own differences in values. Tatsumi might try to make Esdeath see the world in a more positive light, while Esdeath would use her strength to keep Tatsumi safe. It would be a relationship where they both grow and change because of each other.
In a fanfiction where Esdeath and Tatsumi are married, their life could be full of interesting dynamics. Esdeath, with her powerful and often cruel nature, would have to adjust to a more domestic life. Tatsumi, on the other hand, would need to deal with Esdeath's strong personality. Maybe they would have adventures together, with Esdeath using her skills to protect Tatsumi and Tatsumi teaching her about the value of life and kindness. Their relationship could be a mix of love and conflict as they come from very different backgrounds.
A fanfiction about Esdeath and Tatsumi getting married could be really exciting. Esdeath is a very complex character. Her marriage to Tatsumi would mean she has to let go of some of her more extreme ways. Tatsumi, being a hero - like figure, would bring out the softer side of Esdeath. They might have a home together, and Esdeath would have to learn how to cook and take care of the household, which would be a huge change for her. Their story could be about how love can transform even the most hardened of hearts.