Good game.
I am surprised I haven't found it sooner and how for I had to scroll down when I did.
The introduction was a bit disheartening; I love harem games(and you also put that cute little sister there, but no incest), but I still liked it.
Visuals are great; I think there were only a few grammatical errors(which is rare among the AVNs I've seen on Itch); The recap system is nice, it has been a while since I've seen one; I liked what you've done with achievements. All in all an enjoyable experience.
I have a couple of questions though:
The Order was founded ~600 years ago by the previous grand master, after whom the castle is named, so no eternal life with the holy grail but ~600/2 still seems long enough? Not sure how this adds up, but I might have misunderstood something, or you have plans to explain this later(inb4 the old grand master is still alive and turns out to be the main antagonist of the game) .
So with harem not being an option and there being one ending, I take it relationships only affect who(if anyone) is standing next to you in the end? I'm curious, with the how the game is, how do "side-girls" come in play; do you completely avoid them in order to be with one of the main love interests? If you are comfortable answering this question.
Anyway, good work!
Excited to play the finished product(in 10 years I guess).