Iona

Iona is the Mental Model of the Japanese submarine I-401. Mental Models are a simulated, human-like consciousness. And though Mental Models are basically programs, they do possess physical bodies visually almost indistinguishable from that of a normal human. Mental Models were created by the Fleet of Fog, a fleet of unmanned sea vessels primarily consisting of replicas of WW2 era ships equipped with highly advanced technology and weapons. The Fleet of Fog seems to target human sea vessels for reasons unknown. The primary purpose of a Mental Model was to emulate human thought processes and consequently acquire the capacity to strategize and recognize and counter enemy strategies. Iona defected from the Fleet of Fog for initially unknown reasons and now serves as the protagonist's, Gunzou Chihaya's, ship.

Appearance
Iona has long white hair with a light blue tint. Her eyes are sea-green. While in the manga she wears a variety of outfits, in the anime she only wears 2 different kinds of sailor uniforms.

Personality
Iona is usually very quiet. Her face and voice rarely ever betray any sign of emotion, but she does seem to care about her crew and the protagonist in particular.