Board Thread:Questions and Answers/@comment-112.200.103.154-20181007095806/@comment-32952945-20181011102855

He was a human as Ashera and lived with Krul in that time he looked also a little boyish features maybe cause since he was barely resembeling Krul (as a human too).

To be frank when he got turned into a vampire then became a demon it maybe affected his looks drasitcly making him look as Krul brother after she got turned into a vampire

My guess is the transformation changed him completely just so he can look like Krul as you can see in the anime they look almost like sisters when you compare them despite Asuramaru is a male.