Okay, I just finished one of the endings. So I haven't gone through everything yet. But, I have some things to say. I will sound serious, but please don't take it personal.
I think there is a lot to be improved.
First, I really, really like the concept. The idea is brilliant, really. But I believe that it could have been executed better.
Second, the writing. Sometimes I found it to be too... naive. I don't know how old you are and you obviously don't have to answer me. That's your life. But at times I really felt that I was reading a story written by someone under the age of 16 or some age around that. It must have been the way some thoughts, which were meant to be deep and full of meaning, were phrased. Or, it could be a difficulty with the English language. If the case is the latter, it can be forgiven. I myself am not a native English speaker, and often come into trouble while trying to express myself. I don't mean any offense with this.
Way too many, too many typos and grammatical mistakes. I still couldn't believe when at the credits you mentioned that there had been like three proofreaders. I would have expected the grammar to be almost impeccable with that many proofreaders. There were many missing words, and some things were just phrased in awkward ways.
The reason why I care so much about this is that these mistakes, when so frequent, can become a real annoyance. Especially when I'm trying to get in the mood of the characters and enjoy a story that, without the flaws in its writing, would have been truly fantastic. In other words, the mistakes were too distracting, especially when I am so aware of them. o__o
I love the fantasy genre. This is one of the main reasons for downloading this in the first place. I wanted to experience something different. Like I said before, I really like the whole idea. It's very creative.

But we only got to see a town's streets, an inn's indoors, a few outdoor areas, and that's mostly it. Apart from, of course, a few extra places that appeared in important scenes or "flashbacks".
Oh, and practically no descriptions of the surroundings, no details about the world of Fantasia, other than about the conflicts between the different races, and its deities. That was disappointing. Well, the festival is something, but still, not enough. One of the reasons why I like fantasy so much is because I have the opportunity to see new and different things that I know I could never find in the real world. Elves, magic, epic adventures, etc.. Apart from the main characters and the rivals, we only get to interact with a few people of Fantasia. The innkeeper, some townspeople... So in a nutshell, I am still very much clueless about the world of Fantasia. I thought that, the novel being titled "Fantasia, The Realm of Thanos", we would get to see or learn lot more about this fantastic world.
Everything went too fast. It was like, from conversation to conversation. Sometimes, I really wanted a break from that. Like 90% of the game was talking to the guys, and while I know this is an otome game, I think there's still a lot more you could do with this whole idea and the world of Fantasia.
The best part of the story, is obviously the characters. Very well developed. This is one of the strongest points!
As for the graphics, I have nothing to say. I really like the character designs. Perhaps not the best art in terms of application, but it was still very enjoyable and refreshing.

The backgrounds were all pretty nice.
The menu and its backgrounds were great. And so are all the extras. The music was well chosen, too!
And that's all I have to say for the moment, until I finish playing it. Who knows, maybe I'll change my mind about some things once I'm done.
It is possible that, due to my lack of experience with otome games and dating simulators in general, I am expecting too much, detail-wise. I know that the main objective of such games is to win the affection of someone; but wouldn't anybody agree, that a story which takes place in a fictional universe is more enjoyable when you can actually feel like you're part of it, and not just some expectant? I am quite fond of role-playing games and novels (especially fantasy), so maybe there's some influence in my opinion here.

Please accept this as honest, constructive criticism. All I mean is to help.

All in all, I am very glad to have played this. And I'll continue playing some more to see how many different endings I can get and how many more things I can learn about each character and the different relationships. English-language otome games are so hard to find, so like I said, I'm glad.
Thank you for making "Fantasia, The Realm of Thanos"!