The simulators come "empty." You must download song packs (called charts or simfiles) separately.
Link your card to the maimai DX NET website to track your stats and customize your profile from your phone. Important Safety Note Download Maimai
Purchase an Aime or Banapassport card at the arcade. This allows you to "download" and save your personal play data, scores, and unlocks to the cloud. The simulators come "empty
Common sources include the Maimai Simfiles Discord or specialized fan sites. You then move these folders into the levels or songs directory of the app. Download Maimai
If you want to play the "real" game, you don't download it—you find a cabinet.