virtual youtuber shiten'nou
Used to refer to Kizuna AI, Kaguya Luna, Mirai Akari, and Mikoko ("Nojaloli"/Nekomasu) and Siro, in reference to the Shiten'nou (Four Heavenly Kings).
From the List Of Virtual Youtubers:
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 Council" (常任理事国).
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.