Knight: Someone who serves and protects their aspect, and serves and protects others and themselves through their aspect. This is accomplished by either using it as a weapon or making more of it, as there is not only very little of their aspect in their party, but the lack of that aspect defines the biggest struggle of that session.

Heart: Basically soul, the essence of someone's being, and someone's emotions. It's speculated that it's also related to intuition. Heavily associated and likely directly tied to romance and relationships.

So, I think from now on for a knight request I'll start with the last part in the blurb. A Knight of Heart's game session would have very little heart in it. This could mean that their team's hearts aren't really into playing the game, which would be the most fitting interpretation. Their team would suffer because they lack any motivation, and perhaps became apathetic after their previous world came to an end. They would just be dicking around with the alchemiter, not making any progress, or maybe not doing anything at all.

However it could also be that the romantic relationships between different players are so incredibly toxic or tumultuous, or they're so infatuated with each other, that it's impeding the progress of the whole game. This would be fitting for a session that doesn't actually have that many characters. Finally, since Heart is probably related to intuition and gut feelings, it could just mean the players all have shitty intuition, but this seems the least likely.

A Knight of Heart would have similar combat abilities Dirk, and what truly defines them as being of Heart comes from the reasons they fight and the ways it affects the story. They would fight in order to motivate others, or their fighting would inadvertently motivate others. Protecting and the feelings and relationships of those around them would be important to them, meaning a Knight of Heart might end up being an extremely aggressive therapist friend, who uses action to get people to knock off their shit. If someone was being an abusive partner, a Knight of Heart would beat their ass.