I think there are a lot of discrete elements to the found family trope that come together to make it work, and makes it different from just being friends or part of a community or an elite team. So let me go over each of them and talk about how they reinforce each other.
Diversity of Characters. I think AletheiaKnights had it right here. A friend group can come together easily when they all have shared interests and backgrounds, but those become the foundation of those friendships, and those bonds are rarely tested in interesting ways. It’s much more difficult to have a bunch of people with seemingly nothing in common come together, but I think it’s a critical element of the found family. Unique backgrounds, personalities, perspectives. These differences naturally lead to conflict.
Shared Experiences. This is the easiest thing to do with a found family in interactive fiction, and isn’t all that different from other media. The group needs to share intense and challenging experiences that bring them together. The plot of most games is usually enough for this, as you are generally going on an adventure together or working together whether you want to or not, either is fine.
Emotional Depth. This is core to a found family, and separates them from just being an elite team. Elite teams work together to get the job done, pooling their talents and their different backgrounds and perspectives to accomplish goals, but they don’t need to care about eachother as individuals or even have relationships outside of work. A found family must individually care about eachother and explore those personal connections that involve a lot of care and vulnerability.
Growth and evolution. Another critical element of found families. Lots of character have their own arcs, starting as one sort of person and changing over the course of the story, while others are basically the same throughout the journey. Both can work in a found family, but the former is a lot more suited to the concept than the latter. The members of a found family should grow and evolve, individually and as a group.
Sacrifice. Another key difference between fair-weather-friends and found family. The members of a found family should demonstrate their commitment to each other through acts of sacrifice. These sacrifices can range from small acts of kindness to life-altering decisions.
Now that I’ve briefly summarized each point, we can talk about how they all reinforce one another to create a found family.
The Shared Experience is the crucible through which the found family is forged. It provides the circumstances where a group of diverse characters can be forced to work together, even in moments where they might not want to, and opportunities for them to see other perspectives and for their values to clash. These situations help the characters learn to understand and appreciate their differences, work through conflicts, and build trust. It gives them moments of vulnerability they might not have allowed if ever left to their own devices, and allows other members of the found family to treat those moments with care, which helps to create emotional depth. The foundation of the found family becomes their concern for one another as individuals, rather than appreciation of their skills or shared interests. Along the way, they begin to make small sacrifices for one another, and if the bond is strong enough, those sacrifices can become more extreme.
I don’t think any of these things is all that different between interactive fiction or other media, but the major stumbling block is that it is difficult to create a cast of characters that a player can have agency interacting with that will always become a found family. It’s easier to make the rest of the cast a found family and have the player become connected to it, but that tends to cut down on a lot of the things people like about found family as a trope, which includes the journey to becoming one.
I think the Wayhaven Chronicles is one of the better examples of found family here in the CoG catalog.
Diversity of Characters:
Yes, 4 out of 5 members of this found family are Vampires, but they are a very diverse group of individuals even accounting for that. They’re pretty much forced into a team together and make the best of it, though 4/5 have been doing so for a while before the PC gets thrust upon them. While they have the hallmarks of an Elite Team, and two of the initial members of Unit Bravo can be considered friends, I think when you take all of the elements and put them together, they become a very good representation of a found family.
-Adam/Ava is stern, disciplined, and duty-oriented combat expert of the group. Lawful Good.
-Nate/Nat is the diplomat, kind-hearted, understanding, and a calming influence on the team. Lawful or Neutral Good.
-Felix/Farah is outgoing, flirtatious, and brings levity to the group. Chaotic Neutral.
-Mason/Morgan is the prickly and antisocial interrogations expert of the team. Lawful Neutral.
-You, the PC, not a vampire like the rest of the group, initially not part of the shadowy organization they work for, not clued-in like the rest of them. Your personality and skillset can be diverse through the choices you make, but you definitely bring another perspective to the group.
The team comes together to investigate supernatural occurrences in the town of Wayhaven. Over the series, their shared experiences can cause them to butt heads in a number of ways as they work together and sometimes apart to overcome the challenges they’re facing.
Growth and Evolution:
Every member of the team, including the PC, have their own growth arc, which the other members of the team are heavily involved in as the PC comes to terms with the supernatural world’s reality. Their relationships with each other also evolve based on the choices the player makes. The injection of the PC into the group is the catalyst of much of these changes.
It becomes more and more clear over time that the other members of this group are already a found family, and have deep emotional bonds with each other, despite their vast differences. They disagree, they fight, they bicker and challenge one another, but they never fail to come through for each other and the PC is able to glean insight in discussions with them that they understand and care about each other and their differences, they’re (usually) each good at seeing the others’ perspectives and taking them into account even where they disagree, and they make efforts not to hurt one another, though they do occasionally snipe at one another in ways only family can. A lot of the emotional depth comes from the romantic elements, which I will speak more on when we get to Sacrifice.
Depending on the choices of the PC, each member of the group proves time and again that they are ready and willing to sacrifice for each other. From things as minor as putting up with Mason/Morgan’s smoking habit (and understanding the root of it), to risking their lives for each other frequently, to a bunch of other spoilery things, but also crucially represented by the romance options the game presents and made more clear through repeat playthroughs where you explore the different paths the PC can take. Each member of the group can be interested in the PC, and aside from a very well done triangle between the PC, Adam/Ava, and Nate/Nat, they will quickly recognize when another member of the group is forging an emotional bond with the PC, and will immediately step aside and put their own feelings/desires out of mind so that the other can be happy. The Adam/Ava Nate/Nat triangle arises from missed cues and self-sacrifice, where they actually don’t initially recognize that there is something building between the PC and the other member of the triangle, and once Adam/Ava does recognize it, they start pushing the PC away so that Nate/Nat can be happy. The other members of the group check in with the PC as they see things developing more clearly, and it’s clear from those interactions that they worry about each member of the trio getting hurt.