Friender serves as a robotic canine companion across multiple Casshern adaptations, featuring distinct origins and abilities in different iterations. In the original 1973 series, Friender began life as Tetsuya Azuma's pet dog Lucky. Following Lucky's death, his consciousness was transferred into a robotic body. This powerful form granted Friender the ability to transform into vehicles like jets, tanks, submarines, or motorcycles, aiding Casshern in battle. This version also possessed fire-breathing capabilities and demonstrated significant intelligence and combat independence while fighting the Android Army.

The 2008 reboot Casshern Sins presents a different origin. Here, Friender belonged to a young girl named Root (or Wrench) within a robot community peacefully accepting the Ruin. After Casshern destroyed the community during a berserk episode, Friender initially blamed him for Root's death but eventually forgave him. This iteration lacks transformation abilities yet possesses the unique trait of being unaffected by the Ruin. Friender acts as a steadfast companion, actively intervening to halt Casshern's berserk states and protecting allies such as Ringo. He waits alongside Ringo for Casshern's return after Casshern departs to confront Luna.

Personality remains consistent across all versions. Friender exhibits profound, undying loyalty to his masters, whether Casshern or Root. His intelligence manifests through tactical actions like gathering allies to assist Casshern or hunting him for revenge. Bold protective instincts drive him to confront threats, including Casshern himself during violent episodes. Physically, Friender typically appears as a black-plated robotic canine with gold eyes and gray limb joints, featuring ear designs reminiscent of Casshern's helmet. The 1973 design included white and red ears, while Casshern Sins offers a more utilitarian look without vehicular transformation features.

In fighting game appearances such as Tatsunoko vs. Capcom, Friender assists Casshern with special moves. These include aerial dives, ground bites causing extended stun, and flame breath that negates projectiles, reflecting his protective role and combat versatility from the original series.