So after all, Kei Uzuki (Slur) just wanted to kill that bas**** Asaki for what he did in Al Lamar (and we don't know about that yet) and we also saw the past when Sakamoto, Nagumo, Akao and Slur on mission with the leader of the order 8 years ago, and we saw how Asaki threaten Uzuki, by hurting Gaku!! In the Al Lamar Orphanage, that's why Uzuki became a villain because of that, but when I saw his reaction and the feelings he felt during that mission with Sakamoto, Nagumo and Ako made him feel like they trusted him, he did not meant to betray them, but when Ako said something and Slur understand it too, that's the time he totally betrayed them.