I really liked this, the design of the characters are really good, and don't have that bland default koikatsu look. The sex scenes are fluid and not principally not laggy, probably because of the video codec you used. The story has the cliche isekai premise, but, there's nothing wrong with using cliche premises, they just need to be well developed, and from the current state of the game, it looks like it will be well made. Overall, a great introduction for your game! (Also, I've seem you mention about going towards a sandbox approach, i think a more regular visual novel would fit the best, but, i'm not too against sandbox.)