Episode 6: The Mid-Term Test is a Disaster!
Aquamarine (あくあまりね, Akuamarin) is a cat and the familiar of Will.
Unlike Will, Aquamarine is rather calm and reserved. She is the voice of reason in the relationship between her and Will. Aquamarine views Will as very naïve and childish when it comes to his personality and his actions.
Aquamarine remains with Will throughout the story, and in Medical Magical often observes his relationship with Pure, pointing out that he is sweet on her.
Will usually comes up with unexpected or childish decisions which irk Aquamarine. Throughout the series Will tends to come up with ideas and do things his own way, prompting Aquamarine to question what it is that he is planning.