I can explain rather easily. 

The sword is not really special. Besides its color, the durability is only better then normal swords as constant combat would break swords and a better cutting edge purely keeps it from dulling quickly like most medieval swords do. 

His swordsmanship backs up his magic to which he can't just spam magic as it costs quite a bit. While strong in melee combat, it can be lacking mid to long range with his fire spell being the only to have some range to it. 

Only those that choose to be Asura undergo it. It's purely a choice and one that's been going on for hundreds of years. Its not like it's every person and some people in the household take it at older ages aswell. But it's purely their choice and not forced upon the knight in question. 

I'm not using the mythology. Just the word. 

Though I can change whatever. Rather keep the magic swordsman aspect. 

Also since its not accepted yet, I just added in the Fanilly thing so to see how it would be taken first as you told me you wanted to wait and see first.