Risako Niiyama shares a deep history as the childhood friend of Kouichi Hayase and Hideaki Yajima, a connection central to her identity. She is a petite 15-year-old girl with ash-blonde hair, brown eyes, and porcelain skin. Her typical attire is a white school uniform featuring a white skirt and legwear, paired with brown loafers.

Kind and caring by nature, Risako exhibits a protective instinct, especially towards Kouichi. This protectiveness coexists with pronounced jealousy, which flares up over Kouichi's growing closeness with Emi Kizaki. She reacts with frustration or upset when Kouichi distances himself or expresses distrust towards her and Yajima, fueling interpersonal conflicts centered on his attention.

Unspoken romantic feelings for Kouichi remain a constant, unresolved tension throughout her arc, subtly influencing their interactions and driving many of her actions. Initially unaware of Kouichi's involvement with JUDA corporation and his role as the pilot of Linebarrel, her perspective shifts dramatically following Hideaki Yajima's death and subsequent revival.

The secrecy surrounding Yajima's return, maintained by both Kouichi and Yajima, strains her relationships and fosters deep distrust towards Kouichi. Despite her non-combatant background, significant events involving Yajima lead to her eventual integration into the central conflict as part of Hayase's corps, a transition complicated by the persistent secrets between her and Kouichi.