Let me explain this. Any of your servants with SKILL demerit (e.g. Hans, Santera, Ibaraki Lancer and some others more) receive a little buff during this event. I hope this video give you more ideas about what to do (Sadly this one does not apply to Illya because her demerit is in her Np, and you can't add any command cards on them) QUICK P.D.: BUT she can cleanse herself up from her demerits in her NP using her cards, so even she receive a benefit from this Command Card. Remember, this card makes 1 cleanse of any debuff whenever you select that card and use it. So probably, if you run solo Illya, she can cleanse herself from her own demerits after 2 turns in this way: [Turn 1] NP + Command attached card + any other command card. [Turn 2] Select again the command card with cleanse effect + Arts/Buster/Quick + Same. There you go, a lovely nice cleaned Illya.