Forever21 is selling an accessory they call "chain bras." A chain bra is a set of chains that is shaped like a bra and is meant to be worn over a tank top or body suit like a piece of jewelry. Here's an example:
Refinery29 reports that about a year ago, chain bras started emerging as a "festival fashion" trend, and even Bella Hadid was spotted wearing one. This summer, many different chain bras are still available on Forever21's website, leaving us to assume that people must still be buying them.