One of the main themes is acceptance. Michael has to deal with being an alien and Alex has his own set of issues. Fanfictions often show how they accept each other fully. Also, the theme of redemption can be seen. Maybe one of them has made mistakes in the past and they work towards redeeming themselves in the eyes of the other. There's also the theme of family, not just their own families but the family they create together, whether it's a found family or a more traditional one they build over time.
In many of these fanfictions, the theme of sacrifice is present. They might sacrifice their own desires or safety for the sake of the other. For example, Alex could sacrifice his military career for Michael's safety. Another common theme is the exploration of their sexualities. Since both characters have complex sexual identities, fanfictions often explore how they come to terms with it and how it affects their relationship. And of course, the theme of adventure is there as well, as they might go on adventures together, either related to Michael's alien nature or just for the sake of exploring the world around them.
Love and relationship are very common themes. Their complex relationship, whether it's a romantic one or a deep friendship, is often explored. Another theme is dealing with their different backgrounds, like Michael's alien secrets and Alex's family issues.
One great fanfiction could be 'The Bond Beyond Stars'. It beautifully explores the relationship between Alex Manes and Michael Guerin in a post - apocalyptic setting. The story delves deep into their emotions and how they support each other through tough times.
Fanfiction.net is also a good place. There are likely some great stories there. Just make sure to use the search function properly to narrow down your results to the specific characters you're interested in.
One great place to start is Archive of Our Own (AO3). There are numerous fanfictions there about Michael Guerin and Alex Manes. Some popular ones often involve their relationship development, like how they deal with the challenges in their lives while being in love. Another option could be to check out fanfiction forums where fans might share their favorite stories about these two characters.
One common theme could be the relationship dynamics. How the pregnancy affects Alex Manes' relationship with other characters, whether it's his partner, family, or friends. Another theme might be the challenges Alex faces during the pregnancy, like dealing with his own fears and insecurities.
Often, there's the theme of how those around Alex Manes react to his possession. His friends or family might try to save him or figure out what's wrong. There could also be a theme of identity crisis. Alex might not be sure who he is anymore with this other entity inside him. And sometimes, the fanfiction might explore the idea of using his new, possessed state for good or bad, like if he gains new powers from the possession and has to decide how to use them.
One common theme is his past military experiences haunting him. This often causes him emotional and sometimes physical hurt in the fanfictions.
Some fanfics also focus on his role in the overall story arc. For example, how he contributes to the fight against the antagonists or how he helps his friends. This can range from him using his military skills to his more personal qualities like loyalty and determination.
One theme is often the struggle between his human and alien sides. He might have human emotions and values but also alien instincts or powers. This internal conflict can drive the plot in many fanfictions. Also, the theme of secrecy is quite common. Alex has to keep his alien heritage a secret, which can lead to all sorts of tense situations, like nearly being discovered or having to lie to people he cares about.
I'm not sure of specific 'possessed alex manes fanfiction' off the top of my head. You could try searching on fanfiction websites like Archive of Our Own. There are usually a lot of different fanfics related to various characters and themes.
One great 'hurt alex manes fanfiction' is 'Alex's Struggle' which delves deep into his emotional turmoil after a particular incident. It shows his pain and how he overcomes it in a very engaging way.