The game from a visual standpoint is solid, but it has a major flaw: The English translation is rather shoddy. I recommend getting a better translator for future games. For example:
"Since Mom left, I haven't enjoyed any cakes for birthday."
This should be edited to say: "Since mother left, I haven't enjoyed any cake for my birthday."
Note that I used "mother" instead of "Mom", because Nai seems like someone who would use formal wording - if only out of fear for her God. A translation is important, because it forms how the player perceives the world.
Anyhow, the process for learning about Nai and her circumstances could be better handled overall. The scene with her cleaning was good way of demonstrating what her world was like. Unfortunately, most of the early interactions with her were lore dumps. Many words, but artificially placed. Intertwining everyday situations with her damaged persona would work much better.
For example, the first day of her having a meal at the household. Nai would likely be used to her "master" eating first, then feeding a pet, and finally allowing Nai to have scraps and be grateful for it. This is a good way for the player to establish how they treat Nai. Maybe the player does all the work, or perhaps treats Nai as an equal.
The setup for the game is a bit unnatural, such as why police would entrust the player with Nai, and also why Nai's room happens to have women's clothing. While I haven't progressed far into the game, these initial moments stood out to me, because they made me think the game world to be false.
To sum up my feelings: I think the developer has potential, but they need to address their shortcomings to become a good, perhaps even great, hentai game developer.