On the one hand, Wario's employees account for something like 85% of the female characters with recurring speaking roles across the entire Super Mario franchise, but on the other hand, he's canonically violating multiple child labour laws and once stuffed a preteen girl into a cannon and shot her into the sea, so it's tough to say how much credit he really deserves for his equal opportunity hiring practices.
Top: as I previously pointed out in a 2022 post on the Supper Mario Broth twitter.com account, there are extremely few characters with their birthdays explicitly given in official Mario media. One of them is 5-Volt, whose birthday (March 13) was stated once, in a blog post on the 2003 official Japanese website for WarioWare: Mega Microgames. Note that this was before 5-Volt even appeared as a character; the birthday was simply attributed to the then unnamed and unseen "9-Volt's mother" at that point.
Bottom: surprisingly, 20 years later, this obscure snippet of lore was brought back in official capacity on Nintendo's new WarioWare, Inc. portal website, where she mentions that her birthday is March 13. This may be one of the most in-depth pieces of trivia that Nintendo referenced in official material decades after they were first published.
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