The Ikkitousen manga is more extreme than the anime, though the anime is a bit more giving in regards to fully unmitigated oppai.
Ikkitousen manga (20 volumes plus extras, ongoing)
I get the sense that a lot of mangaka begin their new mangas without a clear idea of what they want to do. They fly by the seat of their pants until a few “strengths” of their work become obvious, and then they adjust accordingly. You don’t even have to look very hard to find evidence of this, just look at how different One Piece, Naruto, and Bleach were in their initial arcs compared to the rest of those series.
In the case of Ikkitousen- called Battle Vixens in it’s original manga form- I think the author was genuinely going for an action manga with some fanservice elements very much on the side. The first volume is damn near nipple free, and even the bathing scene is censored. In fact, it’s not until he’s several volumes in before he finally draws nipples in those bathing scenes.
One of the more shocking things I learned when reading Battle Vixens, is that the author (who seems to be a likeable, unabashed pervert himself) basically tip-toes the line as far as lower body nudity is concerned. He’s not afraid to draw buttholes and vaginal creases, there’s even some mosaic action later on.