Age regression- Apparently, the lady on page 320 is a rejuvenated form of the old lady at the start(Kiku-san). Machine translation(I know), about rejuvenation and "Don't make fun of the elderly". I thought it was the other 'greyish' haired lady we see earlier, but she's in the background.
Shame, she only pops up at the very end and isn't in any scenes.