This is the final Part 3 of the series. In Part 1, I built a game in five hours with AI and got rejected by the App Store. In Part 2, I passed review and reached the first penny. Part 3 is the story after launch — marketing, a new tool I started building, and two more experiments already underway.
Day 3 After Launch, I Opened Facebook
I had no illusion that people would just show up after launch, but the first three days were still a bit lonely. Almost no downloads. Instinctively, I posted on Facebook and LinkedIn. Then I opened a Claude chat and asked a simple question — how do I get more downloads for a small game like this? Several answers came back. One of them was that some indie game community contact pages accept app review requests.
Now I send one or two emails a day. At first, it was honestly embarrassing and awkward. I learned that sending a cold email like this was the smallest form of putting down the VP title. But after a few days, a different thought hit me — why didn’t I think of this sooner?
Another Scene from a Decade Ago
When LINE Bubble was hitting tens of millions of downloads in Japan, I personally visited Japanese gaming communities every single day. I watched what was being posted, what people were saying, which games might blow up next. I thought that was a PD’s job. Over a decade later, I realized I was doing the exact same thing for my own side project — right there on an indie community contact page. Tools change, eras change, but the fact that the maker has to walk to where the users are — that stays the same.
YouTube Shorts, and Then I Started Building a Tool
Another method Claude suggested was YouTube Shorts. Unlike other channels, you see real-time reactions the moment you upload. For someone like me who can’t wait, it was a strangely good fit.
Then something else started. I began building a tool to make Shorts videos more easily and efficiently. I’m currently working on about 10 apps and services simultaneously, and I’m designing this tool as a shared module across all of them. The functionality is simple — record a short video of an app running on a real device, edit it, add sound, create subtitles, all driven by LLM prompts. To be clear, this is not a “content auto-generation” tool. It captures and processes real screens from real apps I built. The concept isn’t generating video — it’s prompting an LLM to capture the most compelling scenes of the game on video. This is why I’m building all game scenes in a hybrid architecture.
The fact that I was now building a tool that uses AI, while using AI — that was the most interesting change from a senior’s perspective.
HOL4B.com — In the Meantime, I’ll Focus on This
I should be honest about one thing. I’m currently looking for a job. Ideally, I want to continue in a C-level role at an enterprise company. I don’t know how long that will take. So in the meantime, I decided to give this a real shot. HOL4B.com is the result of that decision. It’s still a mostly empty single-page site, but the plan is to add one line at a time for each product I build going forward. A small workshop for my personal brand.
Version 1.3 and Two More Experiments
Trains Out is gearing up for 1.3.0. The biggest change is on the business side — registering as a business entity and adding a paid ad-removal item. The first in-app purchase button will sit next to the one-penny ad revenue. Two smaller additions: a leaderboard and daily challenges for motivation. I’ll also try to improve the core game feel and rules as much as possible.
And there are two more experiments that have already started.
Gyeol (결 Seoul) — A camera app. I’ve always liked photography, and this time I’m bundling my 10 favorite filters into a camera app. But the core of this app is the 11th filter — an experimental filter that extracts the dominant color of a photo and layers it back over the image. I don’t know if the results will be worth using, but that’s the whole point of a side project. The app is already built, and I’ve been walking around Seoul taking photos to test it in the real world.
Spell Stack — A word-merging game. My kid wanted an app for learning words, so I took that request and layered it onto a 2048-style number-merging mechanic. Instead of numbers, letters combine to form words. Just like Trains Out where my family was the first user, the first user for this one is already decided. It includes grade-level vocabulary curated from public word lists.
So — What Did AI Become for a Senior Developer?
The question I asked at the start of this series was simple. Can AI really code? Can it go all the way to commercialization? After about ten days, one game, and one penny, here’s my answer.
Yes, it’s possible. But AI can’t finish the job alone. Policy reviews (ATT, AdMob child ad ratings), game feel, self-critique, ad appropriateness, marketing that requires walking to where users are — in every one of these areas, a human had to step in repeatedly. But when that human is a 25-year veteran, AI works at a terrifying speed. I could even delegate tool selection, and it still produced results. Working on 10 apps simultaneously, I genuinely feel the power of AI.
There’s a phrase I keep hearing lately. “One-click builders” or “I didn’t touch a single line of code.” That era will come eventually. But having spent ten days living it firsthand, my conclusion is different. Right now, AI is the event of a really good partner appearing for senior developers. Not a tool that replaces someone — a partner that multiplies the judgment seniors have built over a lifetime. I’ve shipped LINE Bubble to #1 in eight countries, and worked across commerce, advertising, mobility, and manufacturing. All those memories are coming alive again through this five hours, this first penny, and these next two experiments. I’ve come to believe again — starting with myself — that seasoned experience isn’t something to be leveled away, but the thing that holds down the far end of the AI era.
This three-part series closes here. Trains Out is still just the beginning. Gyeol and Spell Stack are coming soon. Download links and short gameplay videos are collected on the English launch page.
What You Can Do Right Now
- In the AI era, walk to where your users are. Indie communities, small Facebook groups, company Slack channels — AI won’t take that one step for you.
- Run one side project seriously. You’ll see what AI multiplies for you and what still needs your own hands.
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