Japanese Internet Slang Explained:“Kusa (w),” “Oshi,” and “Numa” — Japanese You Won’t Find in Textbooks

In what situations do people encounter the Japanese language?

Many people learn Japanese through social media or video content, especially if they do not live in Japan or have few opportunities to speak the language. In fact, some of my students mention that they use YouTube as a resource for studying Japanese.

Along these lines, the word “kusa” (grass) can often be seen popping up throughout the comment sections. However, it does not actually refer to grass. It typically appears when someone makes a joke or when something unexpected happens, which can be confusing for those encountering it for the first time.

Expressions like this rarely appear in textbooks, even though they are widely used on social media every day.

In this article, a Japanese teacher introduces three of the most commonly encountered pieces of Japanese internet slang, explaining their meanings and origins. Let’s take a closer look together, starting with expressions that may already feel familiar from online spaces.

“Kusa” refers to something funny or amusing, similar to “LOL” in English. It is often used casually to convey a sense of laughter that is not loud or full-blown, but enough to make someone giggle.

Originally, it started as the expression “(笑),” where the kanji represents laughter. On the internet, it was shortened to “w,” the first letter of the Japanese word 笑い (warai, “laughter”).

Eventually, to express the degree of laughter, it began to be written as “wwwww,” with multiple “w”s connected. The row of “w”s looked like grass growing on the ground, and over time, it started being called 草 (kusa), which literally means “grass.”

In short, the progression is as follows:

(笑) → w → www → 草 (kusa)

It is commonly used casually in comment sections or on social media. Some examples include:

“その発想は草。” —That idea is kusa.  —That idea is hilarious.
“展開が急すぎて草。” —The plot is moving too fast, kusa. — The plot is moving too fast, lol.
“それはさすがに草。” —That’s really kusa. — That’s just too funny.

Alternatively, it can be placed at the end of a sentence or used alone as a comment, such as kusa. Many people write “w,” while others use the kanji 草.

“Oshi” refers to someone or something you especially support or root for. This can include not only idols or actors, but also anime characters, athletes, and sometimes even food. Examples include:

“私の推しはこのアイドルです。” — My oshi is this idol.
“最近、新しい推しができました。” — I recently found a new oshi.
“この店のカレーが推しです。” — The curry at this restaurant is my oshi.

“Oshi” originates from the verb 推す (osu, “to support” or “to recommend”). Originally, idol fans used the term oshi-men, short for oshite-iru member, referring to the member they were especially fans of.

Gradually, “men” disappeared, leaving just oshi, which eventually became a general term.

The progression follows:

推す → 推しメン → 推し.

On Japanese social media, people often talk passionately about the things they like and support. The word oshi is a useful expression that conveys the feeling of “supporting someone” or “caring deeply about something.”

Although the phrase is relatively safe to use, it is better to avoid using it when speaking to superiors or in formal situations. Instead, it sounds more natural to say “my favorite actor” or “an athlete I support.”

You may also come across expressions such as:

“推しが尊い” (Oshi ga tōtoi)— My oshi is precious / My oshi is amazing.
“推し活” (Oshi-katsu)— Activities done for one’s oshi, such as going to concerts or buying merchandise.

Numa (literally “swamp”) refers to a condition where someone becomes deeply absorbed in something and feels unable to get out. The original meaning of numa is a place where it is difficult to escape once you fall in. The slang comes from this image, and it came to describe becoming completely immersed in a hobby, fandom, or piece of media.

“このアニメ、完全に沼です。”— This anime is a total numa.
“気づいたらアイドルの沼にいました。” — Before I knew it, I was in the idol numa.
“一話だけのつもりが、完全に沼でした。”— I only meant to watch one episode, but it turned into a complete numa.

This word is often used together with other nouns, such as:

ドラマ沼 — drama / TV show numa
コスメ沼 — cosmetics / beauty numa
キャラ沼 — character numa

Numa is often used together with oshi, the word we explained earlier. In Japanese online culture, people tend to use words that express a deeper level of attachment or involvement. While oshi is stronger than simply saying “like,” numa conveys something even harder to get out of.

The word numa expresses being addicted to something in an exaggerated and humorous way. It is an interesting expression that playfully conveys the feeling of “wanting to get out, but can’t.”

Numa is basically used in a positive context. It does not carry the nuance of being addicted to something bad or harmful.

In this article, we explored three Japanese slang terms: kusa, oshi, and numa. These words won’t appear in your textbook or on your exam, even though learners encounter them every day on social media. A bit of kusa sprouts in a comment here and there, someone is always talking passionately about their oshi, and there’s always someone deep in a numa. Japanese can be much more playful than you might think!

After reading this article, you won’t be surprised when you see kusa in a comment. You’ll also be able to follow conversations about oshi more naturally, and even if someone falls into a numa, you’ll be able to smile and think, “Ah, this is a fun kind of numa.”

These unique expressions are part of Japanese culture–Japanese isn’t only about serious or formal language. For those who are trying their best to learn Japanese, we encourage you to enjoy a bit of playful Japanese. You don’t have to master everything—simply knowing what these expressions mean can make Japanese social media more approachable and a lot more fun.

At TCJ, we prioritize practical Japanese used in daily life, along with its cultural and contextual background, rather than just teaching textbook Japanese. In the classroom, we solve any questions together with classmates as a group. For private lessons, it’s ideal for those who want to ask about slang they encounter on social media but may feel hesitant to ask about in public.

If you come across any words you see for the first time, just bring them to class. We think through them together while enjoying the learning process, and before you know it, you might find yourself in a Japanese numa—of course, a fun one! You may even feel like, “I want to dive a little deeper.”

Come and explore the playful world of Japanese with us at TCJ!