イオナ, Submarine i-401

She is an anthropomorphic avatar of the Sentoku class I-401 submarine whose sole function is to follow Gunzou Chihaya's orders. It is hinted that two years ago she was programmed, placed on stasis and set adrift by Gunzou's father, Shouzou Chihaya, to wait for his son's arrival in order to awaken and have him take command of her.

Class: i-400-class Attack Submarine (Major Alteration)
Length: 122m Beam: 12m Draft: 10.2m
Displacement: 3545/6575 tons
Mental Model: DualCore G-I x1
Propulsion: Graviton Engine/Type-S x70 Type-R x14
Maximum Speed: more than 60knot (surfaced) more than 80knot (submerged)
Armour: Wave Motion Compulsory Conversion Device Armour