Relationship Arcs: Simulating Years Together (Design Guide)
By Tom | Published on 2025-10-24
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I have always had a fascination with stories. Not the grand epic stories of good and evil, rather the quiet, sprawling stories of everyday life, especially the stories of relationships. How do two people meet, fall in love, build a life and share the decades together? For too long, the idea of capturing that kind of long term journey in an interactive story felt a long way off. But now, thanks to staggering advances in AI and narrative design, we are close to simulating years together, creating profound relationship arcs that somehow feel like they are alive.
In the last couple of years, I have worked deep into the design concepts that make this a reality. We are talking about creating long-horizon narratives, marking the important moments with relationship milestones, and building characters with dynamic memory systems so that they never forget the shared history.
In this deep dive I want to share what I have learnt about how we can design these amazing virtual journeys, the obstacles we face, and the beautiful positive experiences that await.
What is a Relationship Arc?
Think of a character arc, which is the journey of a character's growth. A relationship arc is the same idea but for the relationship between characters. It is the narrative of how a relationship starts, how it develops over the years, based on the shared experiences lived, the choices made, and the unpredictabilities of life. It is not scripted; it is an emergent story. After I've done my research, I've found it helpful to classify these arcs in order to give us a framework for design. Here are some of the most potent types, with emphasis on the positive and enriching journeys we can create.
Types of Relationship Arcs
| Arc Type | Description | Positive Examples in Gaming & Media |
|---|---|---|
| Positive Change | A relationship that begins with strangers or rivals and evolves through shared experiences into a deep, positive bond. | The arc of Commander Shepard and Garrus Vakarian in the Mass Effect series. |
| Positive Steadfast | An initially positive relationship that faces challenges but ultimately grows stronger and more mature. | The relationship between Frodo Baggins and Samwise Gamgee in The Lord of the Rings. |
| Negative Change | An initially positive relationship that deteriorates due to conflict, betrayal, or diverging paths. | The decline between Arthur Morgan and Dutch van der Linde in Red Dead Redemption 2. |
| Negative Steadfast | An initial negative relationship that remains consistently hostile or worsens over time. | — |
| The Constant Rivalry | A steady, long-term hostility between two characters or factions that defines their interactions. | The rivalry between the Empire and the Rebellion in Star Wars. |
| Tragic Arc | A relationship, often positive, that is doomed by external factors or fatal flaws, leading to a poignant ending. | The story of Tidus and Yuna in Final Fantasy X. |
The Blueprint for a Lifetime Virtually
So how do we actually build a system that can simulate a relationship over years virtually? It comes down to three basic design principles which I have spent countless hours exploring: long-horizon narratives, milestones, and dynamic memory.
1. Weaving the Tapestry of Time: Long-Horizon Narratives
In order to simulate years of time, you need to have a story which can stretch and be shaped over a long time. In my experience as a designer, there are two basic philosophies of getting this done:
- Procedural Narrative Generation: this is rather like a storyteller who is in algorithms. The system uses rules to procedurally create events and dialogues, and even entire plotlines, based on the current nature of the relationship. This leads to infinite variety and replay value.
- Emerging Narratives: This is my favorite, but is also the hardest to manage. The story here is not even “generated.” It emerges from the interactions of autonomous characters, a concept explored in papers like Generative Agents: Interactive Simulacra of Human Behavior. Think of The Sims. The story is really the net result of the personalities, goals and interactions of the characters. It is very realistic because, not to put too fine a point on it, it actually is. You can read more about the fundamentals in this excellent article on what is emergent narrative.
| Design Paradigm | Benefits While In Long-Term Sunny Relationship | Drawbacks |
|---|---|---|
| Procedural Narration | Very high replayability; controllable for emotional pacing. | May feel at times generic or repetitious, without careful planning. |
| Emerging Narration | Real original unpredictability in story-telling; very high player immersion. | Hard to control; may lead to boring or incoherent stories. |
2. Marking the Moments that Matter: Milestones
Life is not merely a series of random days but is punctuated by significant events. In relationship science these are referred to as "turning points." In narratology, I call them milestones. These are the narrative cues that give emotional weight to the passage of time.
These milestones may be player-driven in terms of events like marriage proposals, or system-driven such as a career change that adds a stress element to the relationship. The important point is that these events have lasting consequences. Here is how milestones may be occasionally mapped out over a lifetime.
| Phase of Relationship | Possible Positive Milestones | Possible Negative Milestones |
|---|---|---|
| First Spark | A special first meeting, discovering a shared interest. | A misunderstanding, awkwardness at the start. |
| Growing Closer Together | Sharing a secret, overcoming challenges together. | A major disagreement, jealousy from an external source. |
| Commitment | Moving in together, getting married, having a family. | A betrayal of trust, growing apart due to stress. |
| Shared Life Experiences | Celebrating anniversaries, bringing up children, helping each other through illness. | Mid-life crisis, empty nest syndrome. |
| Bonding for Life | Renewing wedding vows, becoming grandparents, looking back on shared life. | Confronting mortality, coping with the challenges of growing old. |
3. The Power of Memory: A Dynamic Memory System
This is where, to my mind, the crux of the matter lies. A relationship that has no shared memory is just a series of unconnected episodes. For a simulated connection to feel real there must be memory.
A sound dynamic memory system is the technological backbone. I think of it in levels:
- Short-Term Memory: "What are we talking about right now?"
- Episodic Memory: "Remember that time we went to the beach when it rained?"
- Semantic Memory: "I know your birthday is in April and that you dislike mushrooms."
- Emotional Memory: "When I think of our wedding day I feel happy. Whenever I think about our big fight, I feel sad.”
These layers come together in the system in such a way that they create a deep, holistic understanding of the relationship’s history, allowing a character to say something like, “You’ve always been there for me since the time you helped me when I was sick,” which is where the magic happens.
My Framework for Designing Your First Relationship Arc
So here is a quick checklist for all you aspiring narrative designers out there to get you started prototyping your own long-term relationship arc.
- Define the Core Arc: Pick your main arc (Positive Change, Redemptive, etc). What is the overall story of this relationship?
- Develop Character Goals: What does each character want? Do their intentions coincide, or conflict?
- Brainstorm Key Milestones: Work out 3-5 significant events that will mark the travel of the relationship.
- Introduce an Antagonistic Force: The antagonist does not need to be a person! It could be a fear, an instance of external pressure that could be a job, or difference in values.
- Develop a Memory system that is simple: Start with variables. A
RelationshipScorewhich can range from -10 to +10 and boolean type flags such ashadFirstFightcan serve to create enormous benefit in early prototypes. - Write Response Dialogues with Consequences: Make sure that decisions are relevant. Consider the benefits real. For example, a kind response could create an increased score, whereas a negative response could flag the character negatively and thereby create an opening for new tense dialogue later on.
- Iterate and Test: Play through it. Is it flowing naturally? Are the milestones carrying weight and meaning? Refinement, refinement, refinement.
The AI Revolution in Action
The most interesting thing happening in this field is now happening with the development of AI companions. I have been watching platforms like Nomi.ai, Candy.ai, and Kupid.ai and they are fascinating case studies on long-term relationship simulation. Their AI is memory-based and dynamic. It retains specific memories from conversations weeks or even months ago, creating in-joke scenarios that let you build a real history together. They become more than simple chatbots and become entities whose personalities grow and adapt to long-term interactions with you. Other platforms like SecretDesires and Sweetdream.ai are also pushing the boundaries of what these multimodal AI companions can do. They provide real evidence that the design principles work.
A Checklist of Positive Outcomes
- Emotional Exploration: Provides a safe avenue for navigating complex emotions and relationship dynamics without real-world consequences.
- Skill Development: Helps people practice empathy, communication, and long-term decision-making.
- Deeper Immersion: A meaningful bond with a character makes every narrative beat feel personal.
- Personalized Stories: Ensures that each player’s experience is unique and co-created with the AI.
- Fighting Loneliness: Offers supportive, nonjudgmental interaction that can ease feelings of isolation.
An Ethical Compass
Of course, with any technology that encroaches on emotions, we need to be wary. There is a responsibility that comes with making AI friendships believable, and that is to ensure that user health is our first priority. There are issues to take into account such as dependency on AI for emotional support, irrational expectations, and privacy of data. As noted in a recent Medium article, Heart Meets Hardware: Unpacking the Ethics of AI Companions.
The impetus is to create systems which model healthy, secure relationships—not ones that manipulate. We need a responsible framework for ethical AI companionship built on openness, user control, and the duty to do no harm.