virtual youtuber shiten'nou
Referred to as the Virtual YouTuber Four Heavenly Kings online (バーチャルYouTuber四天王), and as "Virtual Oyabun and the Four Heavenly Kings" on Pixiv (バーチャル親分と四天王); other names include the Big Four, the "Council of Five Elders" (五大老) and the "Permanent Members" (常任理事国).
Used to refer to Kizuna AI, Kaguya Luna, Mirai Akari, and Mikoko ("Nojaloli"/Nekomasu) and Dennou Shoujo Siro, in reference to the Shiten'nou (Four Heavenly Kings).
The first VTubers to get big, a group originally thought to consist of Kizuna AI, Kaguya Luna, Mirai Akari, and Mikoko. Due to the enormous subscriber gap between her and the rest of her peers, Kizuna ascended past the category (now nicknamed Oyabun, popularized by Luna), allowing Siro to join its ranks. These five would be considered the core, seen as the driving force behind the VTuber boom around the end of 2017 and start of 2018. The title was thus bestowed upon them not necessarily due to them being the Top 5 in subscriber numbers, but as a honorary title by fans recognizing their contributions.
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It could however be said that, with Nekomasu's rejection of the label of VTuber, culminating in his channel rebranding (and being sold) in July 2018, there are once more only four. Two broader versions of the Shiten'nou exist, which, aside from the original five, include either: a) Fujisaki Yua, Fuji Aoi and Tokino Sora, the 8 of them referred to as the VTuber Daisenpai (VTuber大先輩), and the three by themselves as 3JK; b) Tokino Sora and Nora Cat, the 7 of them referred to as the Seven Archangels (７大天使). Aside from Yua, Aoi, Sora and Nora, others who were speculated to be potential candidates back in 2018 were Nekomiya Hinata (at the time one of the biggest frontrunners due to reaching the level of the Big Four), Hibiki Ao, Roboco-san, Koo Furan Zoopaa, Tsukino Mito, and Yomemi. Alongside these were also those considered to be predecessors to VTubers, or Pioneers, such as Chiyu, ILtan, Sayo-chan, Weatheroid Airi and Ami Yamato, as well as Super Sonico, Eilene under ENTUM, etc; whom were not considered actual VTubers unless they had permanently rebranded themselves such.
While it is questionable to speak of new Heavenly Kings from 2018 on due to tradition, several sub-contenders do exist - as an example, Yuikai, Natsumi Moe, Kimino Miya, ProjektMelody, Ironmouse and Hana Macchia as early contenders for the Big Four in (indie) EN spaces due to their early prominence and (for the most part) continued relevance, alongside others such as Deat, Comdost, Mira Pink, Sapphy Stars, the overseas members of WINKS Production, and Beretta Bombshell. Alternatively, Tenkai Tsukasa inhabiting an Oyabun-esque position for Japanese male VTubers.
Following the massive boom in Western interest in VTubing from early 2020 on, particularly benefiting Cover's Hololive, new contenders in the eyes of the West included Inugami Korone (who's garnered worldwide viewership thanks to her memetic moments), Usada Pekora (with the highest viewer count per month of all VTubers), Kiryu Coco (acting as an English-language gateway to VTubers to western viewers), and Gawr Gura (who has since become the biggest VTuber by subscribers in the world), with Akai Haato/Haachama, Mori Calliope and Amelia Watson becoming contenders for Coco's position with her retirement in July 2021. Beyond Hololive, other noteworthy VTubers who contributed to the 2020s boom include Amano Pikamee, Fuzuki Miki, Mint Fantome, Lyrica, girl_dm, and Nyatasha Nyanners (VShojo more broadly). NIJISANJI EN's success (especially in proving the viability of male VTubers in EN spaces through Luxiem/Noctyx) has generally prompted a further rise in interest.