I dont think anyone knows if HH is a MMD creator or not? but what i think everyone knows after reading the letter is, he also helped on modelling and helping Stratovarius stuffs so hopefully he knows what he's doing after working on the project together
oh yea its not UE5,its unity engine judging by the launcher option and the files
It is Unity, and by answering dederath, you can create a scene in MMD, export it to Blender using an add-on, and then throw on it. What kinda explains why all scenes, you can't interact or do whatever.
The port is very old and IIRC deprecated (reason why I think he uses Unity 2017). I got a bit curious and unpacked the whole thing lol.
edit: removal of repetition of word Unity.