Bandai Namco has announced that a free update for Sword Art Online: Fatal Bullet will be available later this month, and will add Sword Art Online Alternative Gun Gale Online‘s M and Fukaziroh as playable characters alongside LLEN and Pitohui.
The update also brings numerous changes and fixes, the details of which are as follows (thanks, Gematsu):

New Additions

Four new characters added (LLEN, Pitohui, Fukaziroh, and M)
Sub-scenarios added for each new character
New costume / accessory added to the shop (Three-Piece Suit M/F)
New costume added to Asuna?s Costume Creation (Vest & Dress Pants M/F)
New faces added to the Avatar Customization (LLEN, Pitohui, Fukaziroh, and M)
Users now receive an in-game e-mail when Prize Rank 10 becomes Rank 1 Kirito?s costume can now be changed

Changes

Maximum level increased from 125 to 150
Adjusted glow effect for characters with buff status
Adjusted ways to receive experience points even when ARfa-sys is not in the party
Adjusted cover vision height
Increased ARfa-sys emotion interval from 15 seconds to 30 seconds
Improved motion and lip-sync actions for ARfa-sys and other characters
Altered fast travel UI
Added fast travel points (Home ?Gallery,? Squadron (PvE) ?Named Enemy Quest,? Squadron (PvP) ?Bounty Quest,? and Squadron (Treasure) ?Treasure Quest?)
Altered sort feature (can now sort weapons by rarity, weapon rank, attack power, weapon rank, shooting type, etc.)
Altered UI on the weapon information screen (adjusted ...