YOTD Chapter 268 Spoilers
This is far fetched and may be unlikely, but what if the sword and shield refer to Soowon and Hak? They’re the two people that elicit the strongest emotions from Yona aside from the dragons. Hak has protected her this entire time, and the story began with Soowon’s sword strike.
It’s interesting that the moment of their touch is highlighted immediately prior to Zeno’s exit from the chalice. Thinking metaphorically, together they represent the body (Soowon as a descendant) and the heart (Hak as Yona’s lover) of the red dragon. Maybe something about their unity is meant to save Yona, the red dragon’s soul?
Here it’s like Hak is saying “I’ll keep Yona and the others safe” (acting as the shield) and, based on Soowon’s thought process, he clearly believes “the rest” to be ending the dragon gods, or maybe severing their connection to Earth so they can’t do more damage (acting as the sword).
Also, Soowon throwing in that tidbit about not being able to do anything to the dragon gods because they’re not people makes me think Zeno (a dragon warrior) needs to get involved. The yellow dragon set itself apart from the others by helping the Happy Hungry Bunch so I bet it’ll play a part as well.