The elite corps Cœur de Fer (Heart of Iron)
Cœur de Fer (Heart of Iron) were a unit of tough Norman-blooded elite crossbowmen who could skillfully hit a target with their bolts and even defended castle walls when heavily outnumbered and no one could join this corps without being vetted in with experience and they were very religious and Catholic zealots. They still carried the blood of their viking ancestors and always operated shirtless during summer military campaigns and they wore little armor so they could move on foot quickly. They were also very skilled at ambushing too and they used horses rarely but in some cases they were used as mounted escorts. They also made good medieval marines often manning ships on voyages and even manned ships and took part in the First holy Crusade.
P.S this is a pure fictional unit in reality.