Iona Kongo, also known as I-402, is a central character in the anime series 'Aoki Hagane no Arpeggio.' She is a sentient humanoid avatar of the Fog submarine I-401. Iona is characterized by her calm demeanor and unwavering loyalty to her captain, Gunzou Chihaya. Throughout the series, she evolves from a weapon of the enigmatic Fog fleet into a key ally of humanity, seeking her own purpose. Her journey is crucial in the battles against other Fog ships, as she embodies the hope for coexistence between humans and the mysterious fleet.