This is part 7 of the Shopaholic Mikuru mini series.
Part 6 is in post #843702.

Wait, isn't it a recurring gag in the series that Mikuru might be older than she pretends to be? So maybe losing 10 years wouldn't be as big a deal.

I can't tell if she freezes because she's getting a mental image of herself as a small child (alongside still-teenaged Koizumi), or if it's because she's trying to think of a way to not answer the question.

Alignn said:
I can't tell if she freezes because she's getting a mental image of herself as a small child (alongside still-teenaged Koizumi), or if it's because she's trying to think of a way to not answer the question.

I think it's a little of both.

It's a running gag in the series that Mikuru's true age is a secret (see also post #850877). Whether she's older or younger than she seems to be, I'm not sure...