Honestly I don't care about sexiness. having a seductive book cover doesn't only work with animé girls. A gorgeous picture of a grass field with knights standing in the wind, would work as well.
A bland book cover on the other hand, cannot attract attention. Worse, it suggests that the story behind would be equally as bland.
In the end I recommend a book cover that advertises your best qualities as an author. If that is your sexy animé characters, then it totally makes sense to have a sexy animé girl as a cover. If that is a sense of wonder and exploration, go for beautiful landscapes. If that is sci-fi and weaponry, go for that.
Whether your story is dark, peaceful, exciting or romantic, your cover should reflect that. It's the best way to catch the good readers through your covers in my mind.