Miso in front, but I asked my question
https://StackOverflow.com/questions/224504

I think takabosoft's response in

is a hint.

// From the navigation controller hierarchy (LowerViewController) to the hierarchy (UpperViewController)
// Prepare a data storage box at the upper level,
let upperView = self.navigationController? .topViewController as! UpperViewController
upperView.box = lowerViewController element
// For presentModal
let parentView = self.presentingViewController? .parent as ParentViewController
parentView.box = childViewController element

You can send a combination of these, but
Isn't it easy to save data in each view?
For example, using Realm.