Kenna Yatsushiro
Yatsushiro is a tomboy, who is considered rougher than the guys. She finds stairs a pain, so she jumps out of windows, and once when she couldn't figure out how to open a door, she destroyed it instead. Despite this, she does have a girly side, as she developed a crush on one of her fellow classmen. She has poor handwriting, but after a week of practice with Kouki Akune, her penmanship improves to a level where she is no longer embarrassed by it. Spoiler Ten years later, Yatsushiro is a calligrapher. (Source: Medaka Box Wiki)