I feel very mixed between giving this a 3 or 4 star because it does a lot of things decently but nothing really well all-around. It's kind of just a frustrating graphic novel, but generally if you want boys love that reads like a more classic European fairy tale, this does that pretty well.
I'm a bit mixed on the art: I'm not a big fan of how Ombra is drawn, and Sirius himself is kind of boring. The extras outside of Mut aren't interesting, either. The mangaka is very good at drawing hands, but some of the pose work is very confusing, and body sizes and expressions are often kind of strange.
I'm reading a translation, so maybe this book is a victim of bad translation, which wouldn't surprise me, given Tokyopop owns the English license. That being said, the writing is kind of dull and meandering. The premise is fun, but it doesn't deliver enough on what it's trying to explain. I would have liked more about how the leads fell in love, in particular, and I felt Wil's evolution was a bit weird. I think a good comparison is "The Genius Puppeteer Loves the Holy Knight Fiercely" by Hatoba Kogarashi, which similarly has some less than great art and wonky writing issues with some forced proximity in a fantasy setting, but makes the whole thing work a lot better.
Despite the difficult topics it addresses, it just feels too soft. And if that's for you, that's great. Unfortunately I found it a bit bland.