I-401, also known as Iona in Kantai Collection, is a fictional personification of the Imperial Japanese Navy submarine I-401. She appears as a calm, polite, and highly capable submarine girl in the franchise. In the series, she serves as a key member of the protagonist group and is central to the naval action and strategic missions. Her role highlights stealth, underwater combat, and the emotional contrast between her gentle personality and the destructive power of war.