No, it's not appropriate. Fanfiction is a creative outlet that should be inclusive. Including sexual content, especially when it involves characters from well - known fictional universes like Loki and Valkyrie, can make many readers uncomfortable. It also goes against the values of a lot of fan - based platforms that aim to promote creativity within the boundaries of good taste and respect for all users.
In general, writing explicit sexual fanfiction is not considered appropriate in most mainstream fanfiction communities. These communities often have rules against adult or inappropriate content to keep the environment accessible and friendly for a wide range of ages and sensibilities. Fanfiction should focus more on exploring characters' relationships, adventures, and personal growth in a more positive and family - friendly way.