No matter what their professional relationship may have been they lucked out on being each other's generation mates. They really brought out the best in each other and the back and forth is absolutely effortless. They're able to play off of each other's strength and weaknesses and made them both stronger as a result.
Shoot, a whole new level of admiration and respect for Maimai just came over me just now...(yeah I know, kinda late huh...) Dang, 11 years old, and she sounded good then already, no wonder it's been more common that new H!P girls list her as their admired senpai.