Fives and Echo

Echo (CT-1409) and Fives (CT-27-5555) are characters in the Star Wars: The Clone Wars universe who served in the Grand Army of the Republic during the conflict. They developed a close friendship during their time together.

Echo
He received his nickname because he repeated all the orders he received.
He cared about his home planet and his clone brothers, for example, he helped in the defense of Kamino, since it was his home planet.
Demonstrated heroism and self-sacrifice to protect comrades and ensure the success of their missions.

Fives
The nickname was "Fifteen" because of his number, which had four fives at the end.
Demonstrated empathy and concern for his clone brothers.
He was brave and courageous in battle.

The story established a close bond between the two characters, which continued even after Fives became the only member of his squad to survive on the Rishi Moon.
Echo and Fives participated in some missions together, such as the rescue of Jedi Master Even Piell from Citadel Prison.
In one episode, Echo helped Fives get out of a difficult situation, and Fives admitted that without Echo, he would have definitely died.
It is also mentioned that Fives was one of three people (along with Captain Rex and Echo) who knew about Rex's battle strategy algorithm.