The basic idea is to have an option to display your most recent incorrect answer to a reading during a review session.
When working through a mountain of reviews, trivial misspellings are pretty common. A “ちょ” can become “ちょう” or “しょ” when you start getting tired, especially if you’re typing on a screen.
Many folks will simply say, “Slow down and see what your error was”, which isn’t wrong of course, but not that helpful when your queue is in the multiple hundreds and you have other things you need to do that day.
I propose simply saving the hiragana on a missed answer and allowing the user to view it when the next prompt for that kanji appears.
Doing that during a single review session would be very helpful, but keeping statistics about missed answers from all your reviews would be amazing (i.e., “You keep misreading [this kanji] as [this misspelling”).