Alrighty then. Please enlighten me.
I'll guess Kytes, who ALSO DOUBLES AS THE VENAT.
My guess is that the Venat (Kytes) wanted to kill Vaan and Reks. He succeeded in killing Reks already by manipulating Basch's twin. Now it was time for Vaan.
And it was Venat (Kytes) who wanted Vaan and Reks dead! But didn't succeed, and instead they were traumatized and experienced amnesia.
D@mn I'm good.