After the breakthrough of Perfume and AKB48, the Japanese music scene around 2010 became a lively battleground dominated by a massive wave of female idol groups. This marked the beginning of what came to be known as the Idol Sengoku period.

Historically, Japan’s Sengoku period refers to the era from the late 15th to the late 16th century, during which regional military powers rose in rebellion against the central government, tearing down existing orders and values in pursuit of territorial expansion through constant warfare. The phrase Idol Sengoku period was coined in reference to this historical context. It was used by media to describe the volatile idol market, where countless groups were born and vanished, while others vied for success by expanding their fanbases, resembling the chaos and competition of the original Sengoku period.

This situation emerged in the wake of AKB48’s commercial success, as talent agencies and record labels across the industry began launching idol groups from every direction. The result was an overlapping of localized fan frenzies that together formed a massive movement. It is also important to note that while the male idol scene had long been a near-monopoly, the female idol market—aside from the long-established Hello! Project—still had plenty of room for new entrants. And it was from this very whirlwind that Momoiro Clover Z rose to stardom.

Now a firmly established force in the idol world, Momoiro Clover Z have not only secured their place as a top-tier group, but each of the four members has found success as a solo artist, actress, or television personality. Just this July, they released their latest track, “Event Horizon.” This year marks 15 years since their major label debut with the May 2010 single Ikuze! Kaitoushoujo—a song that came to symbolize the arrival of the Idol Sengoku period. Even today, the single remains beloved, as shown by the recent remix of the B-side track “Hashire!” and its release on vinyl, mastered by Alex Wharton at Abbey Road Studios.

Momoiro Clover Z was originally formed as Momoiro Clover, before the “Z” was added. The group was launched in May 2008, around the time when Perfume and AKB48 were entering their breakthrough periods. Their agency, Stardust Promotion, Inc., is known for managing many popular actors, and it is assumed that Momoiro Clover was initially created as an extension of talent training for young aspiring actresses.

Because of that, the lineup in the early stages was fluid, and at one point, the group had as many as nine members. Just before the release of their debut single Momoiro Punch in 2009, which was recorded with five members, the group expanded to a six-member unit. At that time, all the members were still in junior high or high school, so their activities mainly took place on Saturdays and Sundays. This gave rise to the catchphrase Weekend Heroines.

Starting with street performances in public parks, the group promoted themselves through grassroots efforts—such as traveling by car across the country to sell CDs by hand at electronics stores. Through tireless performances in small-scale underground live venues, they steadily built up their recognition.

Supported by intense, localized fan enthusiasm, Momoiro Clover made their major label debut in May 2010. The following month, in June, AKB48 held its second General Election, an event where fans voted to decide the group’s singing lineup. This combination of CD sales and fan voting captured national attention, becoming major news. The single that reflected the results, Heavy Rotation, was a massive hit and solidified AKB48 as a full-fledged social phenomenon.

While such mainstream “national idols” were rising to prominence, a series of events in the same year foreshadowed the arrival of the Idol Sengoku period. In May 2010, the popular TV program MUSIC JAPAN aired a special episode focused exclusively on emerging idol groups—an unprecedented move. Then in August, the first-ever TOKYO IDOL FESTIVAL was held with a total of 45 participating groups. Later that same month, the radio station-sponsored event Idol Unit Summer Festival 2010 also took place.

Momoiro Clover performed at all of these events, earning widespread acclaim. Particularly notable was Idol Unit Summer Festival 2010, which marked the first time Hello! Project allowed one of its groups—S/mileage (now ANGERME; active since 2009)—to perform at an outside event. Also participating was SKE48 (active since 2008), part of the AKB48 family. This unprecedented co-appearance of top-tier idol groups helped energize the entire scene.

Even beyond these major festivals, 2010 saw the formation of several prominent groups, including TOKYO GIRLS’ STYLE (active 2010–scheduled to disband in 2026), Sakura Gakuin (2010–2021), and SUPER☆GiRLS. In the same year, Akihabara-born Dempagumi.inc (2008–2025) also made their major label debut. The previous year had already seen the formation of groups such as Shiritsu Ebisu Chugaku, PASSPO☆(2009–2018), and bump.y (2009–2014).

As more fresh new groups emerged simultaneously and live venues began showcasing a wide variety of idols on the same bill, fans found themselves with more and more reasons to get excited. The energy of the “idol otaku” community began to escalate rapidly.

In this way, the on-site performance principle championed by AKB48—who operated their own dedicated theater—was also adopted by many other idol groups who had fewer promotional outlets. The model of performing live shows almost daily, allowing for direct interaction with fans, became the defining format and impression of the live idol scene. This style was firmly established during the Idol Sengoku period.

Absorbing the full intensity of that era’s feverish energy, Momoiro Clover transformed it into the fuel they needed to break free from the chaos of the Sengoku period and take the broader entertainment world by storm. After experiencing a member departure, they rebranded as the five-member Momoiro Clover Z in April 2011. Their debut album Battle and Romance received high praise, and by the end of that same year, they had grown to the point of holding a large-scale concert at Saitama Super Arena for an audience of 10,000.

It should be noted that during this time, on March 11, 2011, the Great East Japan Earthquake struck, causing severe damage to the music industry as well. It would not be a stretch to say that the widespread sense of stagnation and unease caused by the disaster was connected to the simultaneous rise of the idol boom. As a source of energy to blow away everyday anxieties, the playful, cheerful spectacle of Momoiro Clover Z—who called their shows “foolish festivities” (baka-sawagi)—was the perfect fit for the times.

After their breakthrough, Momoiro Clover Z expanded their on-site-first ethos beyond the typical boundaries of live idols. They made appearances at diverse music festivals, including those focused on loud rock and anime songs, proving that their appeal transcended genre and category. Their achievements include opening for Lady Gaga, collaborating with KISS, drawing 60,000 attendees to a 2013 concert at Nissan Stadium, and attracting over 110,000 fans across two days at JAPAN NATIONAL STADIUM in 2014. In 2018, now performing as a four-member group, they held their first concert at the iconic Tokyo Dome. Their activities have continued at a scale rarely seen in the idol world.

It goes without saying that their long-running, spectacular success has served as a powerful source of inspiration for countless idol groups that followed. But it wasn’t just the scale of their achievements that made an impact. The inventive and unpredictable nature of their songs—shaped by producers like Kenichi Maeyamada and NARASAKI (of COALTAR OF THE DEEPERS)—and the rich, playful musicality that expressed their childlike exuberance, were also key to their appeal.

Thanks to the success of their distinctive, genre-defying style, the inherent freedom of the idol format—its ability to incorporate virtually any musical element—began to attract attention from a much wider audience. Idol music, once dismissed as formulaic pop, started to be recognized as a broad and flexible scene capable of embracing a wide array of creative and musical challenges. This shift is undoubtedly one of the major contributions made by Momoiro Clover.

Meanwhile, within their home agency Stardust Promotion, Inc., a series of idol groups emerged as the “younger sisters” of Momoiro Clover. These included the aforementioned Shiritsu Ebisu Chugaku (formed in 2009), TEAM SHACHI (based in Nagoya, active from 2011 to 2025, scheduled for disbandment), Tacoyaki Rainbow (Osaka-based, 2012–2021), Batten Girls (Kyushu, 2015–), and Iginari Tohoku San (Tohoku, 2015–), each rooted in a different region of Japan.

In addition, groups such as Hachimitsu Rocket (2014–2020), Chō Tokimeki Sendenbu (2015–), ukka (2015–), AMEFURASSHI (2018–), and B.O.L.T (2019–2023) have also been formed. Together, these groups have created a vibrant and diverse collective of female idols under the umbrella of STAR PLANET.

Today, the idol scene is no longer commonly referred to as the Sengoku period. Yet within this evolved landscape, the Stardust family continues to command an overwhelming presence.

Writer：Koji Dejima
Japanese music writer. Editor-in-Chief of the Tower Records Japan magazine “bounce”.