My Kodansha dictionary doesn't have 大トリ, but this is what jisho.org says about it: key performer; last performer of the day​. I interpreted it like Yamashiro and Fusou were nervous about having a big role in the festival. I don't know many details about the Zuiun Festival, though, so maybe someone more informed might have an idea.

gufalu said:

My Kodansha dictionary doesn't have 大トリ, but this is what jisho.org says about it: key performer; last performer of the day​. I interpreted it like Yamashiro and Fusou were nervous about having a big role in the festival. I don't know many details about the Zuiun Festival, though, so maybe someone more informed might have an idea.

The wiki says
"Live Event: Yamashiro, are you alright? Zuiun Festival Grand Finale"
"On July 30th, 2017, the final live event gathering called "Yamashiro, are you alright? Zuiun Festival Grand Finale!" will be held."
So it's not about some "big tree", the whole exchange is how they're nervous about being the centerpiece of the closing performance?

Marlin said:

The wiki says
"Live Event: Yamashiro, are you alright? Zuiun Festival Grand Finale"
"On July 30th, 2017, the final live event gathering called "Yamashiro, are you alright? Zuiun Festival Grand Finale!" will be held."
So it's not about some "big tree", the whole exchange is how they're nervous about being the centerpiece of the closing performance?

Ah, I bet that's it then. The Japanese title 【山城、大丈夫？「瑞雲」祭り、大トリよ！】 is similar phrasing to how I interpret Yamashiro's panicked text in the parent post.

So are we gonna change the translation note or not?