Some of the rarest mobile game merchandise, often considered “holy grails” by collectors, can be found on Japanese secondhand marketplaces. These include items like the Arknights 1st Anniversary Art Book, limited-run Genshin Impact Orchestral Concert Music Boxes, and exclusive Comiket doujinshi. The only way to acquire these items internationally is by using a proxy service like Onemall.jp to browse sites like Mercari and Yahoo! Auctions.
In the world of collecting, there are everyday items, and then there are the “holy grails.” These are the legendary pieces—so rare, so beautiful, and so exclusive that finding one feels like completing an epic quest. For fans of mobile games, these grails almost always come from one place: Japan.
You might think these items are impossible to get, locked away forever. But you’d be wrong. Thanks to the Japanese secondhand market and proxy services like Onemall.jp, these legendary treasures are within your reach.
Here are five examples of “holy grail” merchandise that you can actually hunt for.
1. The Arknights 1st Anniversary Art Book (“Rhodes Island’s Records of Originium”)
Why it’s a grail: This isn’t just an art book; it’s a masterpiece. Weighing several pounds, this massive tome came in a beautifully designed collector’s box and was packed with stunning, high-quality illustrations and lore. Its initial print run was extremely limited, and it sold out instantly. Where to find it: Your primary hunting ground is Mercari Japan and Yahoo! Auctions. Be prepared, as its aftermarket price reflects its legendary status, but complete, mint-condition copies appear regularly.
2. The Genshin Impact Orchestral Concert Music Box
Why it’s a grail: To commemorate their live orchestral concerts in Japan, HoYoverse released a series of incredibly intricate, high-quality wooden music boxes, each playing a beloved theme from the game. These were sold almost exclusively at the concert venues. Where to find it: This is a classic “event exclusive.” You will find these on Mercari Japan. Sellers who attended the concerts often list them. Search for 原神 オルゴール (Genshin Music Box) to begin your quest.
3. The Uma Musume “Starting Gate!” Concert Blu-ray Box Set
Why it’s a grail: Uma Musume: Pretty Derby is a cultural phenomenon in Japan, and its voice actresses perform in massive live concerts. The Blu-rays for these events are legendary, often coming with special bonus discs, gorgeous photo books, and sometimes even exclusive in-game codes. The early concert sets are particularly rare. Where to find it: Suruga-ya is an excellent place to check for these, as they specialize in used media. Search for ウマ娘 Blu-ray and look for the limited-edition box sets.
4. Comiket-Exclusive Doujinshi (Fan Comics)
Why it’s a grail: Comiket is the world’s largest comic convention, held twice a year in Tokyo. Famous artists and illustrators (sometimes even the game’s official artists under a pseudonym) release self-published books and comics in extremely limited quantities. A book from a popular artist for a game like Blue Archive or Fate/Grand Order can sell out in minutes. Where to find it: This is Mercari’s specialty. Immediately after Comiket ends, the site is flooded with these rare books. You need a fast proxy service like Onemall.jp to snatch them before someone else does.
5. Any Themed Cafe “Complete Set”
Why it’s a grail: Themed cafes are notorious for selling merchandise in “blind box” or random formats. Getting a full set of acrylic stands or coasters for a game like Ensemble Stars!! without spending a fortune in the cafe itself is nearly impossible. Therefore, a pre-assembled “complete set” on the secondhand market is a true treasure. Where to find it: Search Mercari Japan for the game’s Japanese name + カフェ コンプリート (Cafe Complete). Sellers will often bundle a full set together for serious collectors.
These “holy grails” prove that in the world of collecting, “impossible” is just another word for a challenge. And with the power of Onemall.jp, it’s a challenge you can win.