Ryouka Yamakawa is a 17-year-old female student in Class 5, Grade 2 at Seitetsu Gakuin High School. She serves as a White Kämpfer within a task force created to counter the alliance between Red and Blue Kämpfers. Her initial appearance occurs at the municipal library, with later scenarios featuring her at locations like a hotel pool alongside fellow White Kämpfers.

In her ordinary state, she presents a young idol-like appearance. However, transforming into a Kämpfer shifts her to a significantly more mature, adult-like form. As a Gewehr-type combatant, her primary weapon is an Ingram MAC-10 machine pistol. Her personality starkly contrasts with other White Kämpfers, marked by pronounced insecurity, anxiety, and visible discomfort during missions. She habitually apologizes, often preemptively and with excessive formality, a trait that annoys her teammates.

She avoids malicious actions unless pressured to maintain standing within her faction. While her combat role as a Gewehr user parallels Akane Mishima's function among opposing Kämpfers, their personalities are direct opposites. She operates alongside fellow White Kämpfers Hitomi Minagawa, Rika Ueda, and Sayaka Nakao. Her character appears in the OVA "Für die Liebe," maintaining these established traits and role.