Non-player characters (NPCs) in games have typically followed one rule: players act, and the character reacts – within strict, predefined limits. They often guide a user through a certain story, predefined by a creator. That can be the main storyline, side quest, etc. Even though it can be various, frequently there is not much diversity in the game line through which players go. While it can be fun for the first time, after replaying a game, it becomes boring and even at the start players have limited abilities to go outside the “borders” defined by the developer. That is where AI can help because it can react to almost everything, and this reaction is unique even in the same circumstances. So why not use it in game development to make the final product and user experience even more inspiring!? What happens when that reactivity becomes context-aware, unscripted, and emotionally intelligent?
That’s exactly what a group of Metropolia students set out to explore during the Supercell AI Hackathon, hosted by Junction in Helsinki this May. Their entry, developed in just over 24 hours, landed an impressive 3rd place among nearly 50 international teams and offered a glimpse into the future of interactive AI.
The teammates worked on the Myllypuro campus for two days: on Friday, they brainstormed about ideas and attempted to find inspiration and on Saturday, very active prototype development. After several hours of efficient discussion, they came up with an idea of making the following reactive-NPC prototype:
A game where the player isn’t in control – the AI is
The team’s prototype, Purr-suit of Attention, flips the classic power dynamic between player and NPC. Instead of commanding the world, the player steps into the paws of a curious cat living with an AI-powered fantasy witch – a non-playable character that responds dynamically to everything the cat does. The task of the game is to explain to the AI what the cat wants to use different activities and make the NPC do a certain action.
So, how cat-witch (player to NPC) interaction goes?
- Meow? She speaks.
- Knock over a bottle? She sighs, laughs, or reacts with surprise.
- Jump on a table? She might ignore it, become indignant, or think that the cat is hungry.
Meows, scratching the front door, staring at it for a long time? The NPC will definitely think that the cat wants to go inside, but will she open the door? It depends on the mood and a bunch of other possible factors that cannot be described through “if-else statements”
The twist? None of these reactions are scripted. They’re generated in real time using a large language model, meaning each play through is unique and emotionally rich. And the most impressive thing is that the player has no limits or boundaries! “Cat” can do whatever, and the AI will interpret the player’s actions itself.
How it works?
The system relies on a full-stack integration of modern tools:
1. Unity 6 and C# for gameplay mechanics, API calls and animation control, etc.
2. Python (Flask) for backend logic, handling game events and states, LLM calls;
3. Google Gemini for generating context-aware intent, choosing animation to play and speech.
4. Sesame Voice for natural, spoken responses
Actions taken by the cat are tagged and flagged as events (meow, jump, scrap, etc) and states (looking at and near objects). These are processed by the backend, where the AI evaluates them in context using techniques like high-low temperature, prompt enhancement (system, static and dynamic prompts; moving “IMPORTANT” flag), reattempts, and random selection according to heightening parameters from the AI response. The result? A witch NPC that doesn’t just respond – she feels alive, true (but a little bit “slow-witted person” because the response from free LLM’s API takes some time😊).
The Metropolia team worked closely, handling different roles from backend AI logic to design and animation scripting. The final prototype – developed from scratch in just one day – impressed judges and participants for its creativity, interactivity, and potential for further development.
More Than a Game
The significance of this project goes beyond the podium. It reflects a broader shift happening in AI and game design: toward responsive, emotional, and emergent behavior in digital characters. As large language models become more accessible, fast and controllable, the line between code and personality continues to blur. It isn’t just a whimsical experiment, it’s a prototype for a world where games don’t just entertain – they converse, react, and surprise.
The contents of this blog reflect the collective effort of Metropolia students (Yehor Tereshchenko, Artur Roos, Unai San Segundo, Kartik Patel) participating in the hackathon. With gratitude to Metropolia for giving an opportunity to join from Myllypuro’s co-working places (especially on Saturday), for previous knowledge, and bringing team members together as first-year students; also, thanks to Supercell, Junction, and all participants.
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