"Flight to Salvation" - "The Veil is Torn" [Campaign 4, Mission 2]

Help me with campaign 4, mission 2. I found the Tear of Ashi and defeated the demon in the circle. Now I'm playing as Freya, but I can't defeat the demon when I attack him with a large army. He always has more troops than I do. And I can't ignore him. What should I do?