Despite being considered "slow" and "spacey," Ayumu Kasuga, also known as "Osaka" possesses a unique way of thinking and excels at certain types of riddles. She is part of the "Knuckleheads" group with Tomo and Kagura due to her poor exam performance.  She has a childlike wonder about the world and shares a close friendship with Chiyo, although she tends to get overly focused on certain thoughts and appears absent at times. She's absentminded, and is scared of thunder.