This was a delightful reading experience! It uses a very fun story idea and runs with it using numerous surprises and details.
I didn't encounter any issues running the game. I'm not familiar with VN softlock issues, but if there are worries of bugs during scene transition, a control lock of some kind may help. A back button for dialogues might be harder to add in, but could help in cases of accidental dialogue skips. (None of these happened to me, either, thanks to how otherwise well polished the engine is!)
As for the VN itself, the character art is nice! It's simple, consistent, and colorful. The background art does what it needs to, and the expressions are all phenomenally done. The calm, fun music is also a good fit!
The playful writing was fun to read through as well, of course. There's a good use of certain less popular characters as well as the mansion's own - plus of course the OC herself. I really enjoy seeing how people put OCs in Gensokyo!
The LLM use is acceptable, coming across more as good satire than it does foregoing Wikipedia or other sources - all on top of the explicit context in game. Well done!
Overall, Sumireko's scenario was a perfect fit to the theme, and a very natural use of the environment. Your team did excellent work on this game jam!