Let me try my very best figure out what Arc-V is trying to say
Yuya’s main principles are “smiles” and “entertainment.”
Both of these are challenged with the heavy concept of becoming young soldiers and the idea that people outside of the Standard dimension and that others in general have different life experiences and different ideas of “entertainment.” Whether it’s up to Yuya to challenge that or not is something he has to seriously consider throughout the series.
That could be argued to be a connection to the other conflict happening within Yuya which is his identity crisis. Who is he, Zarc or Yuya? (And also, is he a fighter or an entertainer?)
Arc-V seems to be trying to say that it might be necessary to be both, but to never forget who you really are. To smile through adversity and help others smile in turn is a way to not lose yourself. It doesn’t do any good to put on fake smiles either, like Yuya had done in the beginning of the series, and like Zarc had done in order to please the crowd.
“Just smile” might be sort of the wrong way to put it then, I think, because maybe what Arc-V is really trying to get across is “happiness is something you need to work for sometimes but you’ll achieve your true self when you’re truly happy and vice versa” [”…and happiness can and should be spread, even if only for brief moments”]