Hoshiko first appears in pages 8-9 of Chapter 43 "Part Time Job", where Komi is handing out pocket tissues, and Hoshiko really needs some tissues. Hoshiko sees Komi, but going to get a handout herself is awfully desperate. Komi, a good reader of nonverbal cues, recognizes the strong aura of tissue-needing-ness emanating from Hoshiko, and successful hands out her first pack of pocket tissues.
