The Brief: "Y/N" is used in fanfiction. It stands for "your name" and allows the reader to insert themselves into the story.

DEEP DIVE
“Y/N” is an abbreviation for “your name” in fan fiction. Readers are able to insert themselves into the story where “Y/N” is written.
According to Urban Dictionary, this is used in first person/ reader point of view fanfics. Many of these fanfics are found on Wattpad, Tumblr, and Twitter.
“Y/N” is used often by K-pop stans.
“Y/N” fanfic videos are also popular on TikTok. The hashtag #yn has accumulated over 96 million views on the app.
According to Fanlore, while the popularized usage of “Y/N” is more recent, the term dates back to 2011.
https://twitter.com/byeoldream/status/1286242399417561088?s=20
"Prolog-
"I survive for all this feelings, but i think maybe now i will die, of a broken heart."
-Jinhwan-"My sadness has become an addiction, i feel lost. I start to find my way back which leads me back to my original state: Sadness."
-(Y/n)- pic.twitter.com/QfBFk7KxLp— ThorThor🍒 (@GnaniAu) July 23, 2020
@saladwhyamisalad #greenscreen Guys I was laughing to hard making this, sorry not sorry🤣 #harrystyles #yn #idk #fyp #wattpad