The difference between a “viral hit” and a good ol’ fashioned musical success becomes blurrier every year. Internet culture has gradually just become part of the traditional mainstream zeitgeist, and thanks to digital realities leading  to fractured cultural spaces, the obscure YouTube video enjoyed late at night can now become a year-defining work.

It’s just as true with Japanese music, leading to a lot of questions. Can Kenshi Yonezu’s mega-hit “IRIS OUT” be considered an online-born smash if it was made for a huge anime film, despite some of its key moments basically being tied to .GIF files? Same dilemma with successful anime themes from AiNA THE END and Sakanaction…it spreads on social media, but originates somewhere else. If Mrs. GREEN APPLE are everywhere, are they viral…or just inescapable?

Perhaps a better way to approach it as 2025 comes to an end is to focus purely on surprises that were powered by the internet and felt like left-field surprises. Japanese music over the last 12 months has featured plenty of these, and oftentimes they say something more about where entertainment (and perhaps society) is going. Though sometimes, they are just about frozen treats too.

Just in time to help you sound “with it” at any New Year’s Eve parties you find yourself at, here’s a crash course in the Japanese viral hits of 2025.

Yamino Onesan — “Kiyouikubangumi no Theme”

Japanese entertainment in the 2020s has largely been defined by a glumness towards reality. Ignore galloping rhythms or Technicolor palettes and you find a lot of media commenting on how suffocating society in the country can be. 

That’s the thrust behind “Kiyouikubangumi no Theme,” a chirpy little number that arrived on YouTube at the very start of the year. It riffs on the upbeat theme songs you find on children’s TV shows (specifically the puppet-centric offerings of national broadcaster NHK). Which also explains the above video starring assorted huggable animals who at first glance seem relatively jolly. The lyrics, though, instantly subvert the playhouse atmosphere with a focus on how meaningless and ultimately pointless working can be. Don’t worry if you miss that though — the part where the giant seal starts hurling knives at his fuzzy friends gets the point across.

Millions could relate to those bad vibes and “Kiyouikubangumi no Theme” became the year’s first online hit. That also helped turn the characters associated with the song into something bigger. The YouTube channel behind it continues to share skits that offer a darker turn on family fare, including creepy takes on lo-fi relaxing music. A gacha gacha machine featuring these guys even popped up near my station in early December, showing just how far these depressive dudes have come.

AiScReam — ”Ai Scream!”

While scrmbl already touched on this one, it’s important to note how “Ai Scream!” has remained in the online air as 2026 approaches. Over the last month that’s largely been because of a sprinkling of live performances the trio behind the catchy song have made at events and on TV over the last month. It has also offered the voice-actors-turned-idols a chance to reflect on the genuinely out-of-nowhere success this song has delivered, all thanks to a post-chorus bit that’s easy to imitate and personalize however one wants.

This was the viral J-pop song of 2025, both in terms of how big it got and how many people who might otherwise have no clue about modern Japanese media probably swiped through this one at some point on TikTok. Personally, I’ve talked with people with no idea what’s happening in Japanese entertainment over the last decade let alone the previous 12 months who can do the whole ice-cream-centric-call-and-response bit. Now that’s virality.

M!LK — ”Iijyan”

In mid November, people following NHK’s year-end bonanza Kohaku Uta Gassen got something approaching drama when the debuting artists for the 2025 edition of the long-running show were announced. The K-pop group aespa would be coming over for its first time on the program to perform the hit “Whiplash.” Joining them would be domestic boy band M!LK, whose own huge hit “Iijyan” was accused of ripping off the prior.

Which isn’t really the case and requires something very rare online which is nuance…which makes “Iijyan” one of the year’s most telling breakouts.

Released in March, “Iijyan” is a playful exploration of the idol spectrum. It opens as cliche of a song in this space can get with string swells and sugary all-together-now singing. Midway through though, it flips into the viral part, where “Iijyan” zigs into more aggressive (like, comparatively) dance-pop with house bass and a club thump. This is the part that took off, especially the “Iijyan dance” they do in the video, which filled up short-form video soon after.

It’s that portion that also got clipped and shared online by K-pop fans eager to call out M!LK for ripping off “Whiplash.” Ignoring some bigger details about this — people really think aespa were at the Warehouse behind the decks with Frankie Knuckles or something — this was a great example of a typical failure to actually engage with the whole work, as nobody seemed to have watched the first shiny-shiny part of the number. It’s almost like M!LK is intentionally playing with the extremes of male idol and that maybe, just maybe, that part in the middle is a joke. Then again, hate can be just as potent as love online, and M!LK delivered an online hit by tapping into both.

Mochimochi — “Yaju & U”

The first AI-generated hit in Japan, and one proud of that fact. Channel operator Mochimochi credits song-generating software “Udio” as “Yaju & U’s” composer, and unlike Western efforts at creating fake bands there’s no hesitation in this showing off its unreality. 

It’s a sign of things to come for sure, though there’s also some critical context explaining why this grating number became an online hit and topped domestic viral charts on streaming services. “Yaju & U” is actually all about a 2000s era meme originating from an adult video that gained 2chan infamy for its over-the-top acting. It’s a legendary joke on Japanese video site Nico Nico Douga and one persisting well into today. “Yaju & U” is just referencing this, and in a way feels like half meme and half nostalgia trip for the early days of the internet. 

HALCALI — ”Otsukare Summer”

Speaking of nostalgia…

Aughts rap-pop duo HALCALI scored an unlikely revival hit when its 2003 song “Otsukare Summer” became a surprise favorite of the TikTok set. It’s the latest example of the now-common phenomenon of international audiences dipping into Japan’s vast musical history and finding something they missed (or probably weren’t alive for) and being charmed. The interesting development here is that those with an interest in older Japanese music have ventured into the 21st century, embracing an upbeat rap number that itself is sampling 1950s orchestral records. 

Shinako — ”Unicorn Party”

Less about this specific song being viral and more about the online power wielded by Shinako, the 2020s mutation on Kyary Pamyu Pamyu who has become an inescapable presence on all platforms. This has been underway for a bit now thanks to her variety of content shared online — including a healthy dose of ASMR — but in recent times she has dabbled in a kind of genre-skipping pop that has helped her gain more attention online. “Unicorn Party” with its twinkly verses and EDM drop is just the latest, but she’s also enjoyed plenty of looks for loopy cuts like “Marshmallow Punch” and theatrical collabs with other creators.

This is a good final “viral” sensation to end on because of anything on this list, Shinako has the biggest potential to go even bigger in Japan…if she hasn’t already reached that point. This was a year where she was everywhere online…expect to see her everywhere else soon.