Cross x Regalia (クロス×レガリア) is a Japanese light novel series written by Sanda Makoto (三田誠) who's also the author of Rental Magica, with illustrations by Yuu Gen (ゆーげん), published by Kadokawa Shoten under their Kadokawa Sneaker Bunko label. http://sneakerbunko.jp/series/cross/index.php