Is this Bilena's original plan? Maybe she found out about taming people and the powerup from another book with the star symbol. Wanted to use the power up to overthrow the religious country and free Lily. Found out about mc and his abnormal tamed slime through the guild with her high rank or connections to the capital's guild master.
But is the saintess supposed to be as horny as Bilena? Bilena might want to capture mc since she seems to have a big long term plan for him, but why would Lily sleep with stranger?