How to acquire Prince Thrommel's "damage back" ability?

I recruited Prince Thrommel in temple level 3, and was impressed by his "damage back" ability. Every time a melee enemy damaged him, he was able to cause damage back to the enemy immediately, with a visually sparkling effect.

I'm not sure what the name of the ability is because I mainly focus on playing spellcaster classes. But I would like to let me melee party members have that ability. Is it acquired through feats?

 

It is his sword that has the ability.

 

I understand. Thanks.

 

If the wielder is CG he will get unlimited retaliation attacks , if CN he will get one.
Note that it is a bit bugged if the wielder attacks and takes for example fire damage from lets say a salamander he will keep getting new retaliation attacks and that very often freeze the game.

Good sword though, NG is the best aligment for it as you can use it against all opponents(no retaliation attacks though)

 

Thanks for the info.