@frzned
Pretty sure they're siblings though...
I think the dude definately is since he has the right appearance and seems to be similar in age to them.
The day ain't over yet. The ending definitely feels like a "to be continued". XD
Although @JoshuaDMarti had a good point a bit earlier, that 100% Unrequited Love (the manga) ain't really her thing, since she's living through the real thing pretty much every day.
So it's reasonably likely that her plan was more along the way to arrive at the store and then go like "Oh, but if you're buying it, then can't I just borrow yours later. And then we can use my money to go to a cafe or buy some crepes or something." (I.e. her plan might have been to turn the shopping trip into a proper date.)
This chapter has a lot of Takagi smile screen which I like the most, her pose, the way that she turn around and give a smile, her summer concept. The art become prettier and I didn't notice it, speaking of which, Takagi smile really made my day :333