[... that is a question Ichigo has never thought about. He takes a moment to consider it.]

Well, the most basic definition of a 'brother' in our case, would be those who were crafted by the same swordsmith as yourself. But there is also this deeper and more personal emotional bond, this intense need you feel inside to protect them and love them unconditionally, and you're happy when they are happy. You're also willing to do anything for them.

While a 'comrade' could be anyone we fight alongside with on the battlefield or any of the other swords here. There could be a great level of trust between you and a 'comrade' since we need this trust to be able to work effectively together, but... it's less of a personal connection. It's a more professional connection where we are all working towards the same goal for the sake of our master.

But there are also some 'comrades' that you've managed to build such a strong bond with that they can feel like a 'brother' to you...