A livestream chat is scrolling past too fast to read properly.
The streamer trips over a cable, mid-sentence, and goes down hard.
For about four seconds, the entire chat is one word, over and over: 草 草 草 草 草.
A field has just grown across the screen, and everyone watching knows exactly what it means.
The trail starts with 笑 (warai, "laugh"), the kanji Japanese typists have bracketed after a funny line since the earliest days of email and bulletin boards — the same job the word "laugh" itself was doing. Typing the whole kanji got abbreviated down to its first romanized letter, "w", so a chuckle became (w) and a bigger laugh became (www). Keep stacking w's for emphasis, the way English stacks "hahaha", and a long enough string of them — wwwwwwww — starts to look, if you squint, like a row of blades of grass standing in a field. Someone, somewhere, pointed that out, and the joke calcified into a word: 草, kusa, grass.
Where exactly "somewhere" was is genuinely not settled. The two theories passed around most often point to the anonymous-forum culture of 2ch (now 5ch) and to comment culture on Niconico Douga, the Japanese video site where comments scroll directly across the screen the way subtitles would — a format built, almost by accident, for a one-character reaction everyone can fire off before the clip moves on. Neither claim has a clean paper trail. The w-to-grass visual joke is well documented; which site actually said it first, supposedly, is not.
Once 草 existed as a noun, Japanese did what Japanese always does to a good noun: built a grammar kit around it. 草生える (kusa haeru) — "grass is growing" — describes the state of something being funny, as if the hilarity were visibly sprouting off the screen. Stack the intensity further and you get 大草原 (dai-sougen), "a vast prairie", for something that wrecked an entire chat room, which is the same escalation logic as a single w becoming a whole paragraph of them. The metaphor never broke character. It just kept growing.
Crucially, almost none of this leaves the keyboard. 草 is written slang, not spoken slang — nobody says the word "kusa" out loud to mean "that's funny"; it exists specifically for the gap that typing "lol" fills in English, the reaction you can fire off in one keystroke without breaking the scroll of a chat, a comment thread, or a group chain. Say it out loud at a bar and people will understand you perfectly, and also quietly notice that you are narrating your own text messages.
English speakers assume kaomoji and emoji are where Japanese internet creativity lives, and miss the fact that plain text itself got remade first. 草 is not a pictograph standing in for an emotion — it is a word, with its own verb form and its own grammar of exaggeration, built entirely out of what repeated keystrokes happened to look like on a screen. Grass grew out of the shape of laughter itself, which is a strange thing for a language to do by accident, and an even stranger thing for forty million people to agree to use without ever discussing it out loud.