Buy It: Square Enix
If you're not frightened by expensive price tags, then venture your heart and wallet directly to the Final Fantasy source -- the Square Enix Store. You can find a lot of great merch there, such as items from NieR Automata. Or, more specifically, this red agate and onyx bracelet. Like, how cute is this?
However, the NieR products are only available for pre-order right now, with an unofficial release date of February 2018. So, in addition to the cash you're gonna have to drop for this gift, you'll also have to write a heartfelt "IOU" or a heartfelt "hope you can wait two months, lol."