10.
It isn't their last conversation, but it is a long time before Hatsu initiates another one with her. She didn't need her daughter to help her move, and Ayumu volunteered anyway. It was a nice way to spend his last summer break before middle school.
"Ru-chan would have loved to help too," she mused with a chuckle. "She could see what school she'll be heading to sometime."
"Mom would have told you to keep her." Ayumu sounds too bitter for a teenager. Or just right.
"Don't worry, I'd keep you both."
His shoulders fall with relief. She contains her disappointment.