Oh, the English translation finally got to the introduction of my favorite character in this manga. She's very much like big sister to Mashiro and it's very wholesome.
@Babydel Kind of but not really. Since she's older Mashiro would see her as an Onee-san, though it's more about Mashiro comparing her and Kokosaki together, like for example if two kids would dress similarly they would say that they were twins
@JapanStandard
Just guessing here but I assume the original japanese was 友達のお姉さん
In this case, a better translation would be "a friendly older sister" rather than "the sister of a friend". の can also act grammatically as a adjective modifier (turning 友達 into an adjectival phrase), instead of as a possessive marker (see https://www.japaneseprofessor.com/lessons/beginning/modifying-particle-no/ for a more in-depth explanation). From the context in this case, the "friendly" interpretation seems more likely.
@alliwan
Writing down/showing a page that says I'm mute is kinda redundant when you just can write down what you actually want to say and let others infer from that.