There are no Imperial records of the daemonic entity known as “Temptatrix” before the War for Jenys-S II.
But this malign creature from the warp has a long history with the Eldar race.

As an avatar of its patron-god, Slaanesh, Temptatrix has hunted the Eldar for thousands of years; slaying hundreds on the battlefield, haunting thousands more in their dreams, and even causing Eldar to turn on their brothers and slay each other.

Temptatrix seems to take great delight in corrupting the noble Eldar into giving into temptation and twisting their very souls.
Thus, who can say if the Keeper of Secrets presence on Jenys-S II has more to do with coercing the Alpha Legion into their bidding, or turning the planet into a Daemonworld, or simply providing another opportunity to torment and destroy the Eldar forces there?

Who knows?

But all fear this mighty Daemon Lord of Chaos when it strides the battlefield, scything down its enemies with sweeps of its massive daemon blade.