Some of the mainstream VA's had a career in porn VA, for example lets take Ayako Kawasumi, voice of Saber from Fate franchise's eroge origins, she moved on to other VA work as result of the success over the series, she's done quite the few roles after that in game industry and anime.
Same goes for men, some start with doing some minor VA gigs for otome games, both eroge and all age before the big studios take note of the VA works and hire them for more notable works, you'd be surprised just how many of them start their career as eroge VA.
Most often its the only way to get started in voice acting, if not other means are at hand, even if pays next to nothing.
Or then
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