This series is set about two months after the events ocurred in the Tuatha de Danaan at the end of the original series. Mithril becomes aware of a secret organization that has technology able to counter the ECS (Electronic Cloaking System) mode. This organization, known as Amalgam, also has "Black Technology", obtained from "Whispered" like Kaname Chidori, and like the other intelligency agencies, they intend to obtain more. However, when Sousuke's mission to protect Chidori is terminated by Mithril, all seems to be in place for Amalgam's plans... Like many of its fans know, it is based of the FMP novel "The End of Day by Day."
(Source: Anime News Network)
— Description from AniList community (anilist.co).
