It's highly inappropriate. Such content involving a character from a popular franchise in a nude form is disrespectful and against moral and legal standards.
When it comes to 'How to Train Your Dragon' fanfiction with Astrid lemon, it could mean anything from intense emotional conflicts to bold actions. It all depends on the author's imagination and creativity.
It's all about imagining their adventures in a contemporary setting. You can have them dealing with modern problems while still retaining their dragon-training skills.
To write an Astrid fanfic, focus on her relationships with other characters and build on the existing world. You could have her go on a quest to find a lost artifact related to dragons or have her train a special dragon with unique abilities.
Often, the betrayal could stem from a secret Astrid keeps that accidentally harms Hiccup's interests or trust. Maybe she makes a decision without consulting him that has negative consequences for him.
The likelihood of Astrid being pregnant in How to Train Your Dragon 2 fanfiction is completely up to the creativity of the fanfiction writers. Some might choose to incorporate this element for added drama or character development, while others might not find it relevant to their particular storylines.
Just focus on creating unique and emotional storylines for Astrid's character. Maybe imagine a situation where she faces challenges related to her blindness and overcomes them with the help of her friends and dragons.