The Agita Disc is an old disc containing genetic data used to resurrect the CHAOS siblings (Agita, Anima, Fulmina, Gurgita). It can be found in the storage building of the Laterian Prison.
There are three other CHAOS discs besides this one: the Fulmina Disc, the Gurgita Disc and the Anima Disc. The player can take them to the secondary laboratory at Parum City. If we talk to the scientist from the The Extinction Project quest after collecting the four discs, he'll resurrect the CHAOS siblings and they will start roaming at the Precursor Valley.