So, the art is very nice but the RPG is very hard to play and has a lot of annoyances. I played up to where the koi abandons you and could not defeat the next eye, so I stopped playing.
First of all, the battles all have the same pattern, so they quickly get tedious when it's just buff and attack and heal. There are also a lot of them, with about 5 identical encounters per stage and you often need to defeat all of them to get an item to progress. There's a little bit of story/visual teaser behind each battle, but this isn't enough to make up for the tedium of slogging through 2 minutes of the same strategy. Even the boss battles with the eyes are remarkably similar.
Some other visualaudio annoyances: the save menu has a time delayed popup that makes it very annoying to have to wait for it to disappear to actually exit the menu, or it'll come back up. Defeating the eyes plays a loud and continuous flute attack sound that is painful to listen to. The battle OST is ok, but the experience as a whole makes it grinding and unpleasant which makes me want to stop playing. There are also quite a few typos for important items such as "Repord Card" that should be fixed.
I also think the animation sequences after each boss battle are too long. The art is interesting and nice to look at, but the sequences are just so long and not information is being shown per second, so it gets boring to look at. As a suggestion I think it would be good to break the animations up as post-encounter rewards instead of the black and white images that show for a second that Achille can't quite see, which get a lot less creepy after seeing the same vaguely creepy vaguely unseen images repeated. They may be different but they're not very elucidating, and so kind of blend together. That would reduce the amount of waiting overall.
Of the story I've played so far, I also don't really like the koi. He keeps urging Achille to progress despite Achille's protests, then says this is what Achille really wants when no, Achille's right there protesting all of it saying please help me and don't leave me alone. I don't think he's a good friend not because of supposedly dragging Achille along or not letting Achille grow strong on his own but by his refusal to listen to whatever Achille's saying and instead deciding what he should do for him. This was especially bad when for the third arena the young Achille asks the current Achille to defeat the hands for him, Achille doesn't want to, the koi says he has to, and then Achille is bullied into going along with it, AND THEN the koi says that for some reason they 'have' to do this and Achille 'must' proceed when no, the only one forcing things is the koi. So watching their character interactions ended up with me just shouting in my head SHUT UP AND LISTEN KOI this entire time. I'm also not sure what's up with the monsters and the dreamlike parts, it's all very severe and I think it could help to have some lead up to the more dramatic moments rather than have it all in your face at once. It seems like the abuse Achille's younger selves endures is extreme to the point that it's sort of unrealistic, so I'm not sure if that was a point towards anxiety making fears or experiences into overwhelming suffering. I wish I could've gotten to know Achille himself and his thoughts on his situation more rather than the exact details of bullying, actually. Perhaps there's more resolution after I stopped playing, but I do know that where I stopped playing I left the game feeling drained and confused rather than like I explored someone's mind.