A lantern is a desperate and hopeless situation redeemed, a firework drawing companions close and letting them save the day. It's a sign that even when you feel your weakest, you're not powerless.
It's a memory that can't easily be forgotten. A time of trial and a time of triumph. Lanterns are a comfort now, a hope that burns brightly especially where it's darkest.
Yona's seen candles, lanterns, torches, and the like. But that day in the ocean not far from Awa's port is still a cherished memory, not because she wasn't hurt, exhausted, or feeling powerless, but because even weakness became strength, and they were all fighting beside her in their own way. They were all looking out for each other as well: a team and a family.
Together they all got through it. And Yona knows how deeply they must have trusted her and Yun to let them pretend to be Kumji's goods.
And really as Yona holds a lantern close, it really just gives her a better glimpse of her friends now.