Re:ZERO -Starting Life in Another World- Ex, Vol. 2 (light novel): The Love Song of the Sword Devil 
by Tappei Nagatsuki  (Author), Shinichirou Otsuka (Artist)
When a devil falls for an angel...
Long ago, a great war raged between the royal military of Lugunica and the demi-humans. On that battlefield, a noteworthy young warrior was born---Wilhelm Trias, dubbed the Sword Devil. But despite his skill with a blade, the boy would need to grow much more before he could become a true hero. This is the story of a legendary swordsman--and how he learned to love.