Like many "princess-tier" abyssal ship, she has voluminous extremely long hair and wears a flowing white dress. To her right is a large metal structure shaped like the bow of a WW2-era submarine, except with a trademark toothy maw and glowing eyes. She holds or swims near multiple torpedoes. A pair of tubes also seem to connect into the back of her thighs or butt.
Unlike most of the "princess" or "oni" characters, there doesn't seem to be an obvious single historical reference that Submarine Princess represents, instead seeming to embody all submarines. She has, however, been considered "Albacore Princess" by some, due to the USS Albacore's notorious record against the IJN, although Albacore spent the Solomon Campaign sinking transports, and wouldn't get most of the kills that made the ship notorious until afterwards. There has also been the suggestion that she is I-27, an unimplemented Type-B1 submarine (the same class as Iku/I-19) who sank in the area where she is encountered as a boss.
