There is no official Bandai client for playing Union Arena online. Bandai publishes a teaching app that walks you through the rules, but it doesn't host matches. Everything you can play online today is fan-made and unofficial.
Browser simulators (most active)
The most popular option is Cardboard Kitsune, a free, browser-based Union Arena simulator. There's nothing to download: you build a deck on the site, then play casual or ranked matches against other players, and it also runs community events. It's unofficial and fan-run, so card images and new sets arrive on the developers' schedule, not Bandai's.
A few other fan-made browser simulators exist, some of them playable on mobile. They come and go, so check the Union Arena subreddit or Discord servers for the one your playgroup uses.
Pros and cons
- Pros: free, the full card pool, quick to find a game, and you can test a deck before buying the cards.
- Cons: unofficial, so newly released sets can lag behind; automation quality varies by card; no sanctioned prizes.
Tabletop Simulator
A Union Arena mod exists on the Steam Workshop for Tabletop Simulator, but it hasn't been updated since mid-2024 and is marked as outdated, so it's missing every recent title. Use a browser simulator instead unless your group maintains its own TTS table.
Webcam play
For casual games with friends, plenty of players just point a webcam at their playsheet over Discord. It works with your real cards and needs no software beyond a voice channel.
Where sanctioned play happens
Official play is in person. Local game stores run Union Arena store events, and Bandai's Championship 26-27 season runs Offline Regionals in two waves (Wave 1 from April to July 2026, Wave 2 from August to December 2026), with top players invited to the North America Finals. Event dates and prizes are on Bandai's official Union Arena site.
Getting a deck ready to play online
Build your list in the deck builder: it checks the 50-card, single-title, 4-copy and trigger limits as you go, so you won't load an illegal deck into a simulator. If you don't know where to start, copy a winning list from the tournament decklists and open it in the builder with one click.
Learn the rules first
Simulators automate some steps but assume you know the turn flow. Read the how to play guide for deck rules, card anatomy and triggers, then look up any card you're unsure about in the card database. When you're ready to own a deck, see which starter deck to buy.