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|Novel|| Volume 9, Chapter 7 (First Appearance) |
Volume 10, Chapter 8 (Named)
Iapetus was one of the few members mobilized to support Major Angie Sirius in either capturing or killing Shiba Tatsuya. Iapetus, Mimas, Titan, and Enceladus all appeared when Angie Sirius (Angelina Kudou Shields) screamed, during Tatsuya's first encounter with Angelina as Angie Sirius. While dressed as fake cops they tried to kill Tatsuya for knowing the real identity of Angie Sirius. Iapetus ended up with a serious injury during the fight. 
On the next day, it was doubted whether he would be able to return to the mission. It was said that if he and Mimas could recover enough to move, then they would be sent back to the USNA. 
- In keeping with the naming of USNA Stars members, "Iapetus" is named after Iapetus, Saturn's third largest Moon.