I am not a fan of questions like this myself, but I am really curious and I couldn't find any answers. I searched through the whole OST myself.
I am looking for the music which is often played when the antagonists are plotting something. A good example is Season 1, Episode 19, directly after the Opening, when Raijuta is introduced.
It is quite fast-paced, with a repeating melody, kinda synth-like.