Ichikawa is Matsumoto's daughter, inheriting his role as an advisor to the priestesses and his resistance to Sedna's corruption. Appearing human, she lacks human speech, communicating solely through non-verbal means. Distinctive face markings and hair ribbons mark her appearance.

She shares an island home with Kanon Miyamori, interacting with both human and sea dweller communities. Ichikawa is known for savoring Miyako Miyamori's pickles, a noted personal preference.

Primarily, she offers indirect support to the main characters through her presence and connection to her father. While sharing Matsumoto's resistance to dark influences, she avoids direct combat against Sedna or transformed sea creatures. Ichikawa maintains a consistent presence throughout the story, with her traits and relationships established without significant development or expanded background.