Zwei

Zwei was an astromech R2 unit droid of Rebel commander Ruby Nakamura Rose during the Galactic Civil War and was her trusty sidekick on board her Rose Leader X-wing starfighter that Zwei helped modifiy heavily.

Details
Zwei was much help to Ruby whenever she needed him. He would always sometimes play around and mess with Ruby which made her grow to like and care for Zwei very much. Zwei was a one of a kind R2 unit.

Destruction
It isn't much known on what happened to Zwei after Ruby's death, though remnants of Rose Squadron went looking for him afterwards because he held information that was able to help the restored Rose Squadron. Many within the New Republic Starfighter Corps said that Zwei was destroyed the same time as Ruby's death while some disagreed, saying that Zwei might've taken extra cautions as Ruby would usually tell him too.