Training works as an alternative for Race Moves. Just like it’s used in Inverse World or on the Mage Class. This allows you to play a Fighter of any race, while still beeing different from other Fighters.
Military Training: You were trained in an army or other (semi)organised fighting force. Due to this you learned how to work with your comrades in battle. When you Aid an ally that is attacking an enemy, on a succesful move they take +1d4 damage forward to that attack
Trained under a Master: You studied in one of the great schools of battle under a seasoned master of your style. Because of this you got great insight into the working of combat styles and manuveurs. When you take a moment to study someones fighting style, you can ask “What is the weakness of their style” and the GM will answer you truthfully
Self Trained: You are a savant with the blade, a natural fighter, a child prodigy and worked it all out yourself. Because of that you got to develop a way of fighting that is truely unique to you. When you recruit hirelings, they will accept training in your style as payment.
(that one still needs work but i wanted to present the idea)