Iona, also known as I-401, is a main character in the anime series 'Aoki Hagane no Arpeggio' or 'Arpeggio of Blue Steel'. She is the humanoid avatar of the submarine I-401. Iona possesses a calm and collected demeanor, with a strong sense of duty and loyalty towards her captain, Gunzou Chihaya. Throughout the series, she plays a crucial role in the battles against the Fleet of Fog, showcasing her advanced combat capabilities and strategic thinking. Her journey involves understanding human emotions and forming deep bonds with her companions.