Polaris

 is a gun with three levels. Killing enough enemies with the gun causes it to level up, increasing its damage. However, taking damage decreases the gun's level by 1.

Trivia

 * This gun is a reference to the Polar Star from Cave Story.
 * Cave Story's weapon leveling mechanics are also the inspiration for this weapon's abilities.
 * The "two small tick marks" refers to Quote ("), the main playable character of the game.
 * The synergy is a reference to Curly Brace, a robot character in Cave Story.
 * Its altered appearance due to the synergy is identical to the Machine Gun from the same game, which replaces the Polar Star upon obtaining it from Curly Brace.