There seems to be this weird logic in anime art that as long as any piece of clothing is touching any part of the breasts, the nipple mysteriously vanishes. The sorceress from Dragon's Crown is a big abuser of it too. Realistically, this armor wouldn't hide much. With KLK's style, it's probably best to just look the other way, but it still strikes me as an odd practice.
There seems to be this weird logic in anime art that as long as any piece of clothing is touching any part of the breasts, the nipple mysteriously vanishes. The sorceress from Dragon's Crown is a big abuser of it too. Realistically, this armor wouldn't hide much. With KLK's style, it's probably best to just look the other way, but it still strikes me as an odd practice.
If you think about it Ryuuko's nipples are covered by the silver bits which could be considered hard metal pieces. On the other hand yes you're right it makes no sense on Satsuki's outfit.
In general the practice is there due to nipples specifically being considered the inappropriate part of the breast, rather than the entire thing... (not that it makes sense but that's the general logic...)