Love and relationship development are also prevalent. The 'beast' aspect could add an interesting dynamic, like Link having to protect Ilia from some sort of beast - related danger, which in turn deepens their bond. It could also be that the 'beast' is a metaphor for something within Link or their relationship that they have to overcome together.
You can try fanfic platforms like Archive of Our Own (AO3). It has a large collection of fanfics on various topics, including Link x Ilia from different Zelda series interpretations. Just use the search function and type in 'Link x Ilia' to filter out relevant fanfics.
One common theme is adventure. Link is often on some sort of quest, and Agatha might be involved in that journey, either as a helper or as someone who needs to be rescued. It's in line with the adventurous nature of the Zelda series.
Another reason could be the sense of community. If there are other characters in their world who also read and write fanfiction, it becomes a shared interest. They can discuss their favorite fanfictions, and it helps to strengthen the bonds between them. It also gives them a connection to the creativity of the fans who write these stories, making them feel more involved in the broader fictional universe.
The theme of sacrifice also appears often. Midna has sacrificed a lot in the game, and in fanfics, this idea might be expanded. For example, either Midna or Link might be willing to sacrifice for the other's sake in the context of a new threat or situation. There's also the theme of cultural differences, as Midna is from a different realm. Fanfics might explore how they bridge these differences in their relationship.
One common theme is the struggle for survival. When Link is hurt, he has to fight not only his enemies but also his own weakened state. Another theme is the discovery of inner strength. Through his pain, Link often finds new abilities or a deeper resolve within himself.
Time - travel is a really popular theme. TP Link might travel to BotW Link's time or vice versa. This allows for a lot of interesting scenarios where they have to deal with different cultures, enemies, and ways of life. Also, the theme of shared knowledge is common. For example, TP Link could teach BotW Link about ancient magic that has been lost in BotW's time.
One common theme could be the relationship dynamic between Link and Dark Link. Since it's an MPreg fic, there might be themes of unexpected parenthood and how they deal with it. Another theme could be the contrast between light and dark, as Link represents light and Dark Link represents dark, and how that plays out in the context of a pregnancy.
I'm not sure exactly. Maybe they have some shared characters or a similar theme.
Since I haven't actually read a 'link and ruto lemon fanfic', it's hard to say for sure. But generally in fan fictions about characters from a game like Zelda, common themes could be adventure, friendship, and the characters' growth. However, 'lemon' often implies some sort of romantic or more mature undertones, so there might be themes of budding romance between Link and Ruto.
Since I'm not familiar with specific 'link x pipit fanfic', it's hard to say for sure. But often in fanfics, themes like friendship, adventure, or overcoming challenges are common.