Mascot characters are must if you want to make magical girl series. Sailor Moon has Luna, Sakura has Kero, and Nanoha has her Yuno, mascot characters are self described in their job name, to act as a mascot of the series. Inside the story itself, mascot characters are usually the primeval driving force of a girl’s transformation into a magical girl. They are the trigger of the whole adventure and usually must work double-time as mentor and comic relief character. But as the main audience of magical girl series shift from young girls to creepy otaku, these characters are suddenly viewed as annoyances (take a look a Yuno from Nanoha as example). Suddenly many find mascot characters as obsolete since they have lost their main purpose to entertain (something they aren’t really good at to begin with). Basically they exist solely because of tradition devoid of significant contributions to the story (their presence usually diminish as the series gradually goes on only to reappear in a subplot and return to the back seat again).
And then this bastard came along.