This is set during K-ON!! episode 5 when Azusa and Jun are sleeping over at Ui's place while Yui went to Kyoto. The offscreen speaker is Ui, who is pressuring Azusa to use Yui's toothbrush.
is the artist trying to suggest the existence of an indirect kiss between azusa and Yui happening?
"How is it", you say...It doesn't really taste that different from what I usually use...?That's a relief~... Th-Then, since it's a rare occasion, why not try using this (onee-chan's) toothbrush!?U-Um...H-How is it, Azusa-chan? How does it feel using that (onee-chan's) toothpaste?