The real Pausanias was the ex-lover of Philip II. When the two had a falling out, Attalus raped Pausanias. Attalus avoided punishment from Philip, for whatever reason, which caused Pausanias to hate Philip II even more. It is likely Olympias (and Alexander) approached Pausanias with the promise of revenge.
The real Pausanias was not a man without a heart; the assassination of Philip II was a lover's quarrel exploited by Olympias (and Alexander . . . probably). He tried to run away but tripped on a vine. He was then run-in with a spear by Alexander's close friends. All pathetic-like.
I find it interesting that the mangaka writes out the male homosexual relationships prevalent in Hellenic society at the time. Hephaestion was Alexander's lover but here he is Alexander's alter ego.