English - Koi Breeders - Designer's Diary

2026/9/9 2:37

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Koi Breeders — Designer Diary

Hello! I’m Justin Aguinaldo, the designer of Koi Breeders.

With Game Market approaching, I thought it would be fun to share a little about how Koi Breeders came to be—from its earliest ideas and prototypes to the game it is today.

In this designer diary, I’ll talk about where the idea started, how the game changed through playtesting, and some of the decisions and challenges that shaped its development.

I hope you enjoy this little look behind the scenes of Koi Breeders!

How It Started

I wanted to create a game that combined a few of my favorite mechanisms: trick-taking, bag-building, and auctioning. At the same time, I wanted the game to appeal to both gamers and non-gamers—something light, accessible, and easy for almost anyone to learn.

I’ve always been fond of koi. I’m fascinated by the many different varieties and patterns, and especially by how beautiful they look together in a pond. I’ve also always found the world of koi breeding and the business surrounding it interesting. Eventually, I realized it could make a great theme for a game.

As the design developed, I was pleasantly surprised by how naturally the theme and mechanisms began to work together. Rather than feeling like three separate mechanisms placed into one game, trick-taking, harvesting koi from a bag, and competing for rewards all became different parts of the experience of being a koi breeder.

Development

One of my main concerns during development was figuring out how to make all of these mechanisms work cohesively while keeping the game thematic.

I kept asking myself questions:

How do I connect all three mechanisms?

What advantage should a player get for winning a trick?

How do I keep the game balanced?

How do I encourage players to compete across all three categories instead of focusing on only one?

A lot of the development of Koi Breeders came from trying to answer these questions without making the game more complicated than it needed to be.

Winning the Trick Isn’t the Goal

The trick-taking in Koi Breeders is intentionally very simple. It uses a basic must-follow system, with the highest-ranked card winning the trick.

There’s nothing revolutionary about the trick-taking itself—and that was intentional.

I wanted Koi Breeders to be approachable even for players who have little or no experience with trick-taking games. Since trick-taking is only one part of a game that combines several mechanisms, I decided to keep this part as simple as possible.

In a way, trick-taking is just one piece of the pie.

Winning tricks gives you an advantage, but winning the most tricks isn’t necessarily what wins you the game. What matters is what you do with the koi you harvest along the way.

Designing the Harvest Season

If winning a trick isn’t the ultimate goal, the winner still needs to receive a meaningful advantage.

This became the basis of the Harvest Season.

The winner of each trick gets to draw two koi meeples from the pond bag, while another player gets to draw one koi meeple.

I wanted that second koi reward because I didn’t want harvesting to become too concentrated among only the players who consistently won tricks. By allowing three koi to come out of the pond after each trick, everyone has a better chance of building a collection and having meaningful choices when it comes time to allocate their koi among the game's three categories.

It would be a little sad to reach that part of the game with only two or three koi to choose from!

The Harvest Season didn't always work this way, though.

In an earlier version, the winner of the trick drew two koi from the pond bag, while the player who played the lowest-ranked card of the lead suit drew one koi. The player who played the lowest-ranked card overall would then lead the next trick.

On paper, I liked the idea. High cards could fight to win the trick, while low cards had their own purpose.

But during development, I realized that this created another problem: the high and low cards became too valuable, while the cards in the middle often felt like cards you simply wanted to get rid of.

That wasn't the kind of hand I wanted players to have.

So I changed how the additional koi was awarded, giving those middle-ranked cards more opportunities to compete and making a wider range of cards feel useful.

This was one of the early lessons in developing Koi Breeders: even though the trick-taking rules were deliberately simple, the rewards surrounding each trick could completely change how players valued the cards in their hands.

Designing the Show, Collector & Koi Dealer

I think this is where the real meat of Koi Breeders is.

This is where players start to strategize, deduce what their opponents might have, and even do a little bluffing. For me, it’s undoubtedly the most interesting part of the game.

You might ask yourself:

“Should I put my most valuable koi in the Koi Show? What if someone has an even more valuable koi than I do?”

Or maybe:

“Someone probably has the most valuable koi, but perhaps it’s too obvious for them to enter it in the Show.”

Or you might abandon the Show altogether:

“Maybe I should just put all of my koi into the Koi Dealer.”

You may start out completely confident that you have the best collection, only to look around the table and begin second-guessing yourself.

That uncertainty is something I really enjoy about this part of the game.

Designing the Reward System

Another part of the design that I find interesting is what happens when players tie in a category.

If two or more players have the same value, they cancel each other out for that prize, and the reward passes down to the next highest eligible player.

This was partly a balancing decision. I wanted to encourage players to consider entering a category even when they knew they probably didn't have the most valuable koi.

For example, imagine one player enters a 1-point koi in the Koi Show while all three other players enter 3-point koi. The three 3-point koi tie and cancel each other out, allowing the little 1-point koi to win the Show.

Suddenly, being the underdog isn't necessarily a bad thing.

This creates some fun decisions because having the strongest koi doesn't always guarantee that you'll win. Sometimes you can win by correctly predicting what everyone else is going to do.

And who doesn't love seeing the underdog win?

Koi Show

The Koi Show represents a competition where breeders bring out their very best koi.

The idea here is simple: bring your best koi to the Show.

But because you can enter only one koi, deciding which one to commit—and trying to predict what everyone else will enter—is where the decision becomes interesting.

Collector & Koi Dealer

The Collector and Koi Dealer came from something I found interesting about the real-world koi business.

People from around the world travel to Japan to purchase koi, from individual collectors looking for special fish for their ponds to professional dealers purchasing koi as a business.

I wanted the game to reflect that difference.

A Collector is looking for a smaller, carefully chosen collection, so this category requires only 2 koi.

The Koi Dealer, on the other hand, is in the business of buying and selling koi in larger quantities, so this category requires 3 or more koi.

This gave me three categories that felt different mechanically while still making sense within the theme:

Koi Show — 1 koi
Bring your best individual koi.

Collector — 2 koi
Put together a small, valuable collection.

Koi Dealer — 3 or more koi
Build a larger group of koi for the business.

More importantly, players have to divide the koi they've worked so hard to harvest among these three categories. You can't use the same koi everywhere, so every choice comes with an opportunity cost.

Why Three Seasons?

Koi Breeders is played over three seasons, or three rounds.

I found that three seasons gives players enough time to recover if one season doesn't go their way, while still keeping the overall game light and relatively quick.

It also gives players time to learn about each other.

After the first season, you may begin to notice how another player approaches the three categories. Maybe someone consistently puts their strongest koi in the Show. Maybe another player prefers to avoid the obvious competition and focus on the Dealer.

By the second and third seasons, you're not just thinking about the koi in front of you anymore. You're also thinking about the other breeders at the table and the habits you've seen them develop.

The Game I Wanted Koi Breeders to Become

More than anything, I wanted Koi Breeders to be a game that almost anyone could enjoy.

I wanted families to be able to play it together. I wanted to be able to bring it out with friends who play a lot of board games, but also with people who don't.

I didn't want it to feel intimidating.

The trick-taking is deliberately simple. The koi are colorful and tactile. The rules are approachable. But underneath that simplicity, I wanted there to be enough room for players to strategize, read their opponents, take risks, and occasionally pull off an unexpected win.

A light game, but not a thoughtless one.

That, ultimately, is what I wanted Koi Breeders to become.

That, ultimately, is what I wanted Koi Breeders to become.

See You at Game Market!

Bringing Koi Breeders to Game Market in Japan feels especially meaningful to me. Koi are such an important part of Japanese culture, and I'm excited—and a little nervous!—to finally share my game with players in Japan.

If you get a chance to play Koi Breeders at Game Market, I hope you'll enjoy raising your koi, competing with the other breeders, and maybe even seeing a little 1-point koi unexpectedly become the champion of the Show.

Thank you for reading about the story behind Koi Breeders.

I hope to see you at Game Market!