Part of me suspects botting, but it's also worth noting that V4Mirai's debuts have gotten bigger every gen.
The Lunalia (Gen 3) girls were sitting at roughly 15K subs each just before debut, and have continued to grow, albeit at a slower pace:
View attachment 78824
Petalight (Gen 2) didn't even hit 10K until a couple of months after debut. But compared to Lunalia, they didn't get much promotion.
By contrast, Lunalia and now Voltail are getting boosted hard with all the ads and announced watchalongs. 40K pre-debut is a bit crazy, but not excessively so when you consider ads + watchalongs + established V4Mirai fanbase + broader Brave/corpo fanbase.
Still 40K pre-debut is the highest so far for Brave's EN operations. Previously, it was VSPO EN where they had about 30K subs pre-debut. It probably helps that the other Brave EN corpos are up and running. It helps boost engagement and the overall footprint of these debuts more. Back when Petalight debuted, it was just V4Mirai.
For reference, highest Lunalia debut CCV was Nova, who peaked at 6K, while averaging 4K (the peak was brief, and doesn't really reflect in the chart). Everyone else averaged around 3K:
View attachment 78827