Well, this is interesting. Apparently the English translation is the DLC, and it's currently incomplete. Once you reach the end of the beach section the game ends. So yeah, this is DLC 1, and they're hinting at future DLCs, in theory they're supposed to be free but who knows. This is not announced in the Steam page btw.
Not only that, I've checked other games by this publisher. Fan communication seems to be very lacking on Steam, essentially sending you a Discord link or an email to communicate with them if you want to report something. Also, all of their releases are censored, and seeing how this is a Japanese publisher, it's going to 100% stay that way if you care about uncensored stuff.
That it's a JP publisher also kinda explains the MTL, they probably have no idea how to translate from JP to English so they just did the lazy thing of using machine translation and barely put any effort into editing, which explains why there's JP symbols still in some parts and why there's inconsistencies in the names. This also explains some bug reports I see in the games that are not supposed to be there, things weren't properly checked after applying the translation.
So yeah, this is one of those publishers. The ones that port JP games to Steam by doing zero effort whatsoever for a quick cash grab.