The recruitment Envelopes and/or application slips featured in the Gacha (Game Mechanic) pulls in Blue Archive. They are delivered by Arona (Blue Archive) and/or Plana (Blue Archive) in exchange of the player's Pyroxene (Blue Archive)s.
They come in three colors depending on their rarity: Blue for one star characters; Yellow for two stars; and Purple, the most rare, for three stars.