Alongside Utsutsu and Inpei Seant, Soso was ordered by an unnamed marshal to create clone monsters for military strength after Ultraman's departure. Alongside Utsutsu, the two created clones of Kemur, Gomora and Bullton. According to Soso, although it is possible to clone Zetton, he choose not to do it out of fear that the monster cannot be controlled. Alongside Utsutsu, Soso would eventually defected from the military after Bullton caused the dimensional tear that brought multiple monsters and aliens to Earth. He also administered his marshal with a cell that turned him into Jamila.
When Dark Zagi appeared, Soso and Utsutsu wished to become kings of the new world and in turn transformed into Dark Giants. Soso becomes Dark Mephisto and Utsutsu becomes Dark Faust as they wreak havoc on the city. When Akiko Fuji challenge them as Giant Soldier F, Mephisto summoned Jamila as their aid but said monster was killed by Ide via Mars 133. The two engaged in the battle against Fuji but neither of them are proficient fighters due to being children and scientists. Zagi joined them and managed to weaken F but once all three of them open fire on Fuji, her Mefilas Bot radiated and in turn transform her into Ultraman F. The female Ultra counter their attacks by killing Faust with Specium Ray and Mephisto with M87 Ray. After Zagi's death, Mephisto try to commit suicide by detonating the Earth with him until he peacefully left when Utsutsu's spirit plead him not to do it.
Powers and Weapons
- Genius-level Intellect: Soso is evidently one of the young prodigies who is capable of mastering the science of cloning.
- Although their age is unspecified, Soso and Utsutsu's status as young Ultra Hosts may parallel with Yuuto Tamaki or around those of Hikaru Raido. In fact, they are also the first to be aligned with darkness.
- It is hinted that instead of simple transformation, Soso and Utsutsu traded their humanity to transform into Dark Giants, thus making it clear that the giants themselves are their current forms.
- How they obtained their Dark Giant forms from Zagi is based on the old German literature where a man named Faustian exchange his soul with the devil in exchange for unlimited knowledge. Surprisingly, all three people in question are researchers themselves.
- It is heavily hinted that Utsutsu is Soso's love interest, since her death nearly drives him to suicide.