|Office of Secret Intelligence|
|Founder(s)||Charles zi Britannia|
|Headquarters||Underneath Ashford Academy|
| Rolo Lamperouge |
|First Appearance||The Day a Demon Awakens|
The Office of Secret Intelligence is an intelligence agency answerable only to the Emperor, tasked, among other tasks befitting a secret agency, with the capture of C.C. Its members appear not to have been informed of C.C.'s immortality, and only a few selected agents have been disclosed to the true power of Geass.
The OSI was created in 2017 for some unknown purposes. It was infiltrated by Orpheus Zevon who was affiliated with a terrorist group Peace Mark during the Black Knights and Glinda Knights conflict in Ashford Academy.
The Agency in 2018 was tasked by the Emperor to monitor Lelouch and to search for the whereabouts of C.C. After the tampering of Lelouch's memory by Emperor Charles, Lelouch is kept under constant surveillance without him ever noticing, a testament to their secretive nature. The Agency also kept tab of every one Lelouch's activities whether it's waking up in the morning to skipping classes and they kept the detailed information inside a journal, which one Agent of the OSI described as a "Breeding Log" and regarded Lelouch as nothing more than "bait" or a "trap" to capture C.C.
The OSI Base is secretly hidden inside Ashford Academy, the entrance to the OSI is located behind a bookshelf. The bookshelf is a disguised door to an elevator that goes underground, where headquarters of the OSI is located. Most Agents of the OSI are well disguised as teachers or as members of the school staff and some are disguised as a civilians, but some OSI members can also be seen in which can be safely assumed as their uniform.
Under the leadership of Villetta Nu, the OSI was tasked to monitor Lelouch's activity and capture C.C. for the Emperor, but after she restores his memory and his Geass power, Lelouch manages to infiltrate the headquarters and also persuaded Rolo to join his side. With Rolo's help, Lelouch successfully blackmailed Villetta in exchange for her silence. From then on, Villetta was forced to serve him and he also used his Geass on several of its other members, putting the entire OSI under his control. When Suzaku reached the OSI and talked to its members, he realizes that the entire staff has been put under Lelouch's influence. After Lelouch's ascension to the throne it is not revealed what happened to the OSI. It was revealed by Viletta that the OSI's cameras no longer functioned meaning that the OSI is now defunct.