Bleg for a serious weaboo power

This is little add-on for the latest ReLIFE manga chapter, 139. What does it mean, "英世は折ってはいけない"? I understand that she must not break something, but what? And why is it nostalgic? Scanlation's translation makes no sense. Google was no help thus far. Neither were official dictionaries.

UPDATE: The best guess so far is that Hideyo may be an as-yet-unintroduced member of the preparationary committee. The only problem is, why no honorific?

UPDATE: Never mind, false alarm. I remembered the reference. She means the 1,000 yen note that Arata told her not to fold.