I always wonder how a solo developer can source high quality assets like these, plus develop a full game with them. In this case did the dev create the assets or did they purchase them from a freelancer? How much would purchasing this many assets cost?
Anecdote, but I recall my friend saying he worked on freelancing assets to some train game and showed me some pictures of the said game. Unless there are more of these in existence, I think it was this.
It wouldn't surprise me if Japan has its own market for train assets. There's a big community of train simulators! Go to the Kyoto or Tokyo train museums, they have dozens where you step into a replica of a train cab and then drive a photorealistic simulation (sometimes also just film) - the ex-keyboarder for Casiopeia runs a train simulation game company that makes those since the 90s (https://en.wikipedia.org/wiki/Minoru_Mukaiya). There are some Nintendo Switch train simulators like Densha de GO that are only available in Japan.
I'm sure there's a treasure trove of already-built high-quality assets of Japanese trains.
I thought it was kind of commoditised these days - there's an Unreal asset store I think? Probably one for Unity as well.
Almost every time I see a halfway polished “solo developer” game, they did not do all the work themselves. Especially, they usually hire out the music, maybe other sounds, and much of the artwork. Sometimes they also have freelancers doing marketing and such. Sometimes even some paid help writing the software.
I highlight this not to bring those developers down, but because I think it’s important people understand how these things actually come to be, so they aren’t discouraged to try themselves by thinking they ought to actually be doing 100% of the work solo. That’s pretty rare.