User blog comment:Kaido King of the Beasts/Chapter 870: There and Back Again/@comment-24850639-20170629162723/@comment-24769684-20170629164152

I think Oda had Reiju threatened because she's the only one that's been portrayed sympathetically, thus it means something for Sanji and Luffy to go out there. If any of the brothers were under attack, I'd be like "hell yeah, whoop their asses Big Mom!"

Not to mention that Reiju seemed pretty fine and determined after the explosion, so she didn't feel like a typical damsel in distress.