Aasu Masamune, often called by the nickname Earth Masamune, is a character from the anime Lonely Castle in the Mirror. He attends Yukishina Junior High School as a second-year student. Originating from the year 2011, he becomes the fifth person to arrive at the castle after passing through the mirror's portal. A dedicated video game enthusiast, this passion is a core part of his identity. His enthusiasm for gaming directly inspires another character, Subaru Nagahisa, to pursue a career as a video game designer.