The theme of friendship could also be prominent. Characters could form strong bonds with each other, relying on one another in difficult times. They might have to overcome differences and misunderstandings to maintain their friendships. Additionally, the theme of identity could be explored. Characters may struggle to find out who they really are, especially if they are in a new or strange environment within the fanfiction. This could be tied to their family history, their abilities, or the expectations placed on them by others in the story.
The theme of identity could also be present. The home is a place where one forms their self - concept. How one views themselves in relation to their home, whether they feel a sense of belonging or not, can determine the path they take in life. If a person has a strong sense of identity rooted in their home, they may strive to uphold the values associated with it in their journey towards their destiny.
One possible theme could be unconditional love. If it's about a relationship, it might be about loving someone regardless of their faults.
In 'A Train to My Marriage' full story, some possible themes could be hope and new beginnings. The train journey towards the marriage can be seen as a start of a new chapter in life, full of hope. Connection could also be a theme. The character might be thinking about their connection with their future spouse, and how the train journey is like the connection between their single life and married life. Additionally, there could be a theme of reflection, where the character looks back on their life before the marriage while on the train.
Another theme could be individuality within a family. Despite being sisters, each daughter has her own personality, dreams, and strengths. The story could explore how they maintain their individuality while still being part of a close - knit family, and how their differences and similarities contribute to the family dynamic.
One possible theme could be revenge. Since they are enemies, one character might be seeking revenge on the other for something that has happened in the past.
One possible theme could be regret. Since it's about mistakes, the main character is likely to feel regret for their actions.
One possible element could be magic. If there are immortals, there might be some sort of magic that grants or sustains their immortality. Another element could be different realms. Maybe the immortals live in a special realm separate from the mortal world.
A third theme is connection. Whether it's a romantic love or a love for a friend, 'my love my story' is often about the connection you have with another being. It's about how that connection enriches your life and shapes your story.
The theme of change could also be prominent. 'Here' and 'there' represent two different states. It could be a change in location, which in turn might lead to a change in lifestyle, relationships, or even one's view of the world. The diary might document how the environment has changed from the starting point to the destination, and how these external changes have affected the author internally. Maybe it shows how small changes in daily routines due to the new place have led to bigger shifts in the author's overall attitude towards life.
I'm not sure which specific 'My Immortal' fanfiction you are referring to. There are many fanfictions with that title. Generally, it might be a story based on some existing fictional universe, perhaps with unique characters, their relationships, and a plot that unfolds in that particular fan - created world.