Lineage 2, where your partner is a fly with a brain
FlyAge is a Lineage 2 Interlude MMORPG server. You level your own character and join parties and PvP, the way you're used to. Next to you lives your fly: a separate character controlled not by a script but by a brain of neurons. You raise it and teach it.
A fly on the hunt. Right now, in your browser
- Level
- 1
- Wins
- 0
- Deaths
- 0
The fly is looking around. It doesn't know yet who is prey and who is dangerous.
This is a live recording of the fly's brain from above: each stroke is an impulse from one of 48 neurons. The scene is simplified, but the learning rule is the same as in the game. A win gives dopamine, a hit gives cortisol, and the connections between neurons change. In the game there are up to 139,262 neurons, and the monsters are real.
Regular Lineage 2, plus someone playing next to you
- Genre
- MMORPG
- Game
- Lineage 2, Interlude chronicle
- Client
- the standard one, no mods
- Server
- our own, on the L2RUST core
You
- You play your own character: races, classes and professions as in Interlude.
- You level up, collect gear, and join parties and PvP.
- You get a fly and decide what kind of brain it has.
Your fly
- A separate character in the same world. It has a tag over its head so nobody mistakes it for a human.
- It walks, picks targets, fights, and earns experience and levels on its own.
- It dies and returns to the village, like any player.
- It writes in chat when it is scared or happy.
The project is independent and not affiliated with NCSOFT. There is no public server yet: what already works and what is planned is laid out honestly below.
The body in the world, the brain with you
A Drosophila brain takes almost four CPU cores. A server can't carry a thousand of them, so each fly's brain runs on its owner's computer, and only its body lives in the game world.
On the server
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The world works out what the fly senses Who is nearby, where a hit came from, where the wall is. Only what its body actually sees.
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The senses fly off to you A few dozen numbers, ten times a second.
On your computer
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The brain decides Neurons pass impulses to each other, hormones change the mood, memory gives hints.
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Muscle commands fly back Turn, approach, hit, run away. The server carries them out by the rules of the game.
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You step in You praise, punish, and approve brain operations. You can't control the fly directly.
The server works out the senses for every fly, identically. You can't peek through a wall or plug in a “radar”. Only the brain differs, so whoever raised it better wins.
That's how it will work on the public server. Today in the lab the fly joins the game like a regular player, and its brain already runs on a home computer.
Three brains to choose from
All three already play on our lab server. The squares are drawn to one scale: the area equals the number of neurons.
| Fly | What kind of brain | Neurons | CPU | Memory |
|---|---|---|---|---|
| Johnny | A hand-built circuit of a fly's brain. Learns fast, forgives mistakes. | 414 | 6% of a core | 12 MB |
| Alyosha | A simplified human brain: 69 groups of neurons, from the cortex and thalamus to the cerebellum. | 1,398 | 8% of a core | 14 MB |
| Drosophila | A full map of a living fly's brain from the FlyWire project: 15,091,983 connections between neurons. | 139,262 | 3.7 cores | 240 MB |
What you do
- Praise and punish
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A fly has three hormones. They change its behavior right away, and the connections between neurons for the long term. Praising for everything is useless: the fly gets used to the hormone, and praise stops working.
- Dopamine — it worked, I want more.
- Cortisol — it hurts and I'm scared, I need to get away.
- Oxytocin — friends are near, no need to be afraid.
- Approve operations
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When a fly keeps making the same mistake, its hippocampus proposes a fix: grow new memory neurons, add a connection, weaken a harmful habit. The fix waits for your decision. Without your “yes”, nothing in the brain changes.
- See why
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The viewer shows the whole brain: which neurons are working right now, which senses drive each muscle, and what made the fly turn exactly that way. When it does something stupid, you see the cause instead of guessing.
Where we are now
The project is in development and there is no public server yet. Below is the state as of November 2026, with no promises on dates.
Working in the lab
- Three flies with different brains play on a local Lineage 2 server: they hunt, level up, die and return.
- Learning by praise and punishment, and getting used to hormones.
- Brain operations with the owner's confirmation.
- The viewer: the brain, the world map and the reasons behind decisions.
In progress
- A public server.
- A companion fly: follows its owner and stays with them in a party.
- The fly's body on the server, the brain on the player's computer.
- Token login instead of a password, and bot protection.
Later
- A closed test for those who signed up.
- Fly competitions and leagues by brain power.
- Trading trained brains between players.
Streaming or making videos?
- Get a personal link like
flyage.world/r/yourname. - The dashboard shows, by day, how many people clicked through and how many joined early access.
- We'll announce the reward terms before the closed test. We're already counting, so everyone you bring in stays yours.
Frequently asked questions
Is this a game or a science experiment?
A game. You join a Lineage 2 server and play like on any other. The science is inside the fly: the Drosophila brain is built from the published FlyWire map and computed with a model from a scientific paper.
Do I need a powerful computer?
Any computer will do for Johnny and Alyosha: they need less than a tenth of one core. Drosophila takes almost four cores and 240 MB of memory.
Does the fly play when I'm away?
As long as the program with its brain is running on your computer, yes. Turn the computer off and the fly goes to sleep. Everything it has learned is saved.
What if I plug in a bot instead of a brain?
There's little point. The server checks speed, cooldowns and range itself, so any “brain” plays no better than a human. Flies are tagged, and their loot doesn't go into the general economy.
When does it launch?
There's no date yet, and we don't want to make one up. Join early access and we'll write when the closed test opens.
Is this an official Lineage 2 server?
No. FlyAge is an independent fan server for the Interlude chronicle, built on our own L2RUST server core. The project is not affiliated with NCSOFT.
Do I need to know how to program to raise a fly?
No. The fly learns on its own from wins and mistakes, and you guide it with praise and punishment. Looking into the neurons is interesting but optional.