I'm not sure of specific 'failsafe x guardian destiny fanfic' off the top of my head. But you could also try reaching out to the Destiny fan community on Reddit or Discord. They are usually very helpful in pointing out great fanfics, and someone might be able to recommend a really good one in this particular pairing.
Adventure and survival are likely themes. In the Destiny universe, there are always threats. So in these fanfics, the guardian and Failsafe might team up to face some great danger, like a new powerful enemy or a cataclysmic event. This would make for an exciting read as they use their unique abilities to get through tough situations.
There are many 'destiny fallen x guardian fanfic' out there. Some are action - packed, like those where the fallen and the guardian are in the middle of a big battle against a common enemy. In these stories, you can expect a lot of exciting fight scenes and strategic planning. Others are more character - driven. They focus on the personal growth of the characters involved. For instance, a fallen who starts to question its own motives after interacting with a guardian, or a guardian who becomes more empathetic towards the fallen race through their encounters.
One popular 'Destiny female fallen x guardian fanfic' could be 'The Unlikely Alliance'. It explores the relationship between a female fallen and a guardian in a post - apocalyptic world filled with challenges. They start off as enemies but gradually form a bond as they realize they have common goals in the fight against greater threats.
One popular 'Destiny' female guardian fanfiction is 'The Guardian's Ascent'. It focuses on a female guardian's journey to master new powers. Another great one is 'Among the Stars: A Female Guardian's Tale' which details her adventures across different planets in the Destiny universe.
Another place could be FanFiction.net. There are many writers on that platform who are into Destiny and might have written stories about a Guardian and a Fallen. However, the quality can vary, so you might need to sift through a bit. But it's definitely worth a shot.
Alliance is also a theme. The idea of a Guardian and a Fallen teaming up against a greater threat, perhaps something that endangers both of their species. This can lead to some exciting adventure - type stories.
One common theme is redemption. Often, the fallen are portrayed as having a chance to be redeemed through their interactions with the guardians. Another theme is cooperation, as they have to work together despite their differences. And of course, there's the theme of discovery, both in terms of learning about each other's cultures and abilities.
One great 'destiny reader x stranger fanfic' is 'A New Destiny'. It has an interesting plot where the reader character meets the stranger in a very unexpected way. The author does a great job of building the relationship between them slowly.
One interesting story could be about a Fallen Captain and a Guardian who are forced to team up against a common enemy. They start off distrusting each other but as they face challenges, they gradually come to respect one another's skills.
One common theme is the idea of redemption. The female fallen often has a past filled with actions that may be considered wrong, but through her relationship with the guardian, she finds a path to redemption. For example, she might have been involved in raids against the guardians before but now is fighting on their side.