After many scenes, you will be in control of Snow again. Kill off the PSICOM operatives and be prepared for your first Eidolon battle! Examine the tutorial in detail and the fight will go smoothly.
Eidolon Battle Tutorial: More Info
Eidolon Battle: Shiva Sisters
Nix will be doing the attacking, Stiria will be doing the healing. Make Snow a SEN and keep using the Steelguard command - the best time to use it is just before Nix strikes you with any of her attacks. Do not worry about taking damage, Stiria will heal you frequently. You can only die if the Doom counter reaches zero.
Instrument of Flight
Slipped through the net and lived to fight another day.