Gothy Moon and Coach EastStern are two of Ruby Sword's very few friends before he met Adagio and later Sunset, and opened up even more, and the three of them are rather close, EastStern having encouraged Ruby to pursue his interest in martial arts when he was young and him respecting and caring for her deeply, while Gothy he met thanks to EastStern and struck up a somewhat surprising but strong friendship with!
When the three of them together we have EastStern as a bratty, hothead teacher who usually acts before she thinks or declares she's going to do something or teach someone a lesson, and Gothy Moon encourages and enables Easty with her insane energy and support and plans and magic… while Ruby Sword is the mildy grumpy/stoic and slightly overprotective voice of (usually ignored) reason that usually has to clean up their messes or protect them from the consequences or themselves.