If you're into collecting hard-to-get Nintendo items, this is probably one of them: Nintendo Game Boy Drawstring Pouch DMG-06 ソフトケース. For a while the only reference image I knew of was the one hosted on https://maru-chang.com/hard/gb/english.htm.
While I don't own one, I was able to gather some images which should help collectors in their hunt for Nintendo accessories. I've also saved Yahoo Auctions Japan listing as a PDF for reference.
LKP (last known price) 14,000円 which is about $130!
DMG-06 ソフトケース & Japanese barcode T4902370500936 manufactured for Nintendo by Belleseime.
Visit this link for higher resolution images https://imageevent.com/gamescans/consolehardware
