In my story, the MC and his best friend are introduced as such as soon as the story begins. They have grown up together, facing the hardships of a training facility for super-human children. It takes place eh, 300-ish years in the future on Mars, and I need a word that they use exclusively to address each other. Something like "bro" or "buddy". I could just use "bro" or "buddy" but with how frequently slang changes generation to generation I doubt they will be around in 300 years. Plus those words are just boring... Any suggestions?