I believe that to be understandable! She is your sister after all! It's your duty as an older brother to watch out for her safety!

[He hopes that the Naegi siblings at least reunite back home. It sounds likely at least! From what he knows, both of them are still alive.]

I-I promise, Naegi-kun. It'll be a promise between men, so neither of us can back down from it, no matter what happens!

[Even the Mondo in the candle's smoke seems to be fired up.]