|Spoiler Alert: This page contains spoilers. Read at your own risk.|
The Fortress Series (城塞・シリーズ), also known as Burg Folge (ブルク・フォルゲ) was developed in Germany, which became the first time the technique of tuning Magicians via genetic manipulation was used in the world. 
Burg Folge is the name given to those who had their the body tuned with a technique developed with the emphasis of improving the durability of the body. Due in part because Magicians were thought to be weaker at close range combat instead of at magic. They underwent the strengthening of their physical abilities contained in their genes, which brought forth a breed of "Super soldiers that could use magic", or "Enhanced humans that could simultaneously use both superhuman physical abilities, and magic technical abilities", both of which were more apt descriptions than calling them tuned Magicians. 
When one didn't remove the body’s limiter through any external means —— it was already known at that time that such a method would have a high probability of damaging an individuals magical technical ability —— but by raising the performance of the individuals physical body. Possibly as a result of the unreasonable genetic remodeling, many among the Burg Folge's First Generation died during childhood, and even the majority of those who grew up to become adults either went mad and died.  The mind of those who were young had a high rate of self-destruction, but those who were Third Type's had a ten percent increase in stability over going mad. 
Leo‘s grandfather, Georg Ostburg, is known to be one of the few survivors.