This gallery is focused on illustrations of girls in acts of intentional and unintentional breast exposure, but especially the unintentional kind where an errant nipple is accidentally exposed to great erotic effect, called 胸ちら / munechira.
The contents of the gallery are rather similar to the previous, though photographic, clothing failure ero gallery, so you can readily compare the two.
I must admit to preferring the 2D version, especially considering some of the beautiful images present, but there is also something to be said for the spontaneity of the photographs. There is also the matter of skirt failure, although rather than clothing failure as such, I rather think these are defective by design.
This surprised me when I saw it was animated (enlarge).