It is catchphrase of character okada akane in response to her imagining about nemoto hina
It comes in 2 variety
1 the initial one was when Akane shocked for the first time and immediately shout ひな――――――!!!
2 the next appearance in manga was when she saw dildo in sex toy store where she says Hina’s name (ひなぁ...) while having empty eyes https://watamote.fandom.com/wiki/WataMote_Chapter_139
ctrl + f "Okada is more surprised with Hina's reaction", her face I am referring to is below the panel in the image provided by wikia
Yes all uploaded by me. Last time I ask about snitch tag, this is
the forum's response