Midorikawa Hikaru, nicknamed by fans as Guririba (from "green river", literal translation of his last name) is one of the most prolific JP voice actors right now. You'll run into him in about 90% of anime, games and the like.
About the CAD giving voice actor info in many of my missions: it's either because the cast is a major selling point of the work (Onmyōji), the work doesn't make that big of a deal about the cast (this one, whose voice credits are given in official literature but not the game itself) and thus it's given to help the readers and myself remember, or because I just like to geek out about JP voice actors.
On Ina's fascination with Vil Schoenheit (CV: Aiba Hiroki): the guy is hot and pretty, I won't deny, but Ina likes him because of the character's life philosophy – Mr Fairest-One-of-All believes that a man who's not traditionally masculine is not less of a man, and being cute, pretty and delicate aren't weak traits.
P.S: True confessions: ever since starting twst, my portrayal of 'Guya is a weeee bit influenced by Vil. Sure, he's still a yamato nadeshiko, but he's written as doing makeup and other beauty-related things a bit more often. His counterpart in the Heian AU is partially meant to evoke the Evil Queen.