They can do whatever they want. It's called artistic license. They don't have to adapt the manga because the original story is not in a manga; it's in a light novel.
Clearly their intent was to mimic the manga because it looks almost equivalent. I don't agree that they "tried to tone down the sexiness". They kept it all intact in terms of what they showed "on camera" and where they were focused, and only obscured the nipples so that they could air it on TV.
No, they are pretty different. ---
I want a pet Lavos Spawn. [Order of the Cetaceans: Phocoena dioptrica]