We studied dynamics of O⁺ ions during the superstorm that occurred on 29–31 October 2003, using energetic (9–210 keV/e) ion flux data obtained by the energetic particle and ion composition (EPIC) instrument on board the Geotail satellite and neutral atom data in the energy range of 10 eV to a few keV acquired by the low-energy neutral atom (LENA) imager on board the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite. Since the low-energy neutral atoms are created from the outflowing ionospheric ions by the charge exchange process, we could examine variations of ionospheric ion outflow with the IMAGE/LENA data. In the near-Earth plasma sheet of X _GSM ∼ −6 R _E to −8.5 R _E , we found that the H⁺ energy density showed no distinctive differences between the superstorm and quiet intervals (1–10 keV cm⁻³), while the O⁺ energy density increased from 0.05–3 keV cm⁻³ during the quiet intervals to ∼100 keV cm⁻³ during the superstorm. The O⁺/H⁺ energy density ratio reached 10–20 near the storm maximum, which is the largest ratio in the near-Earth plasma sheet ever observed by Geotail, indicating more than 90% of O⁺ in the total energy density. We argued that such extreme increase of the O⁺/H⁺ energy density ratio during the October 2003 superstorm was due to mass-dependent acceleration of ions by storm-time substorms as well as an additional supply of O⁺ ions from the ionosphere to the plasma sheet. We compared the ion composition between the ring current and the near-Earth plasma sheet reported by previous studies and found that they are rather similar. On the basis of the similarity, we estimated that the ring current had the O⁺/H⁺ energy density ratio as large as 10–20 for the October 2003 superstorm.