Lion Heart

Lion Heart is a firearm.

Source
Lion Heart is available in the main game after completing Episode Prompto.

Trivia

 * There are many weapons named Lion Heart that appear throughout the Final Fantasy series. The foremost, and arguably most iconic, is the gunblade wielded by Squall Leonhart in FFVIII. The blue accents on the FFXV revolver are likely a reference to the blue blade of Squall's gunblade.