A frequent theme is miscommunication. In many of these fanfictions, Harry and Tonks don't communicate their true feelings properly, which causes misunderstandings and ultimately heartbreak. Also, the theme of sacrifice is there. They might sacrifice their relationship for the greater good of the wizarding world, like Tonks might put her duty to the Order of the Phoenix above her love for Harry.
The theme of social and age differences also plays a part. Harry is much younger than Tonks, and in the wizarding society, this can create a barrier. Their different social standings and the expectations that come with them can lead to a breakdown in their relationship. These differences are often explored in the context of their heartbreak in the fanfiction.
One common theme is friendship. Given their age difference and different roles in the wizarding world, a platonic but strong friendship can be a central theme.
There's a fanfic called 'Broken Hearts in Hogwarts'. It focuses on how Harry and Tonks' relationship goes wrong. Tonks' feelings for Harry are strong, but things like the ongoing battle against Voldemort and Harry's own preoccupations get in the way, leading to heartbreak for both of them. It's a really sad but well - written piece.
One common theme could be self - discovery. Since it involves a different take on the characters, fem Harry might be on a journey to discover her new identity and how she relates to Tonks in this new dynamic. Another theme could be the exploration of their relationship against the backdrop of the Harry Potter universe, like how they deal with the magical world's challenges together.
One common theme is family. Andromeda comes from the Black family, and exploring how her family ties and her own choices (like marrying a Muggle - born) impact her relationship with others in the Harry Potter world, including any potential connection to Harry, is often explored.
One common theme is acceptance. Remus has to accept his own identity as a werewolf and Tonks has to accept the challenges that come with loving him. For example, in many fanfictions, Remus is initially hesitant about being with Tonks because of his condition.
One common theme is the struggle against prejudice. Since they are an unusual couple in the wizarding world, they often face judgment from others.
One common theme is the idea of finding love in the midst of chaos. Given the war - torn world they live in, their love can be a haven. Another is the exploration of Tonks' unique abilities as a Metamorphmagus and how that adds an interesting dynamic to their relationship. For example, she might change her appearance to make Harry laugh or to show her different moods related to their relationship.
A major theme is the exploration of their unique magical abilities. Tonks' Metamorphmagus ability and Harry's connection to Voldemort are often used as plot devices. For example, some fanfictions have Tonks using her ability to help Harry in some way. Also, the theme of sacrifice is common. Since both are in the fight against the Dark side, they may have to sacrifice things for the greater good in these stories.
The theme of self - discovery is also present. Through the betrothal, Harry and Tonks learn more about themselves. They discover new aspects of their personalities, their likes and dislikes, and how they can grow as individuals while being in this unique relationship. This is often shown through their interactions with each other and how they face challenges together.
Often, there could be a theme related to Tonks' identity as a metamorphmagus and how that affects her pregnancy. Maybe she has to be careful not to accidentally change her form in a way that could harm the baby. Also, the theme of protecting the unborn child from the various threats in the wizarding world, like dark wizards or magical creatures, could be present in these fanfictions.