The two were once part of Organization XIII, but were mercilessly killed and/or converged with the original Keyblade master, Sora.
Also, this term is directly related to butt-smex. XDDD
Roxas: No one would miss me. *fangirl teardrop*
Axel: You can't go against the Organization!!! >_<
Axel: Gimme, gimme, gimme a man of the midnight! Won't somebody help me chase the shadows awaaaaaaaaaaaay~!
Roxas: Wtf is Akuroku...? *types in on Google* JESUS CHRIST!!!!!
The name is derived from the Japanese names for Axel and Roxas, AKUseru and ROKUsasu, respectively.