Orrin's trick.
The latest episode subtly revealed a new part of Orrin's ability, one that explains how Orrin is going to lose.
Specifically in the moment after Orrin captures Sera, we see John comment on the defenses dropping. So its heavily implied in this moment that his ability can buff those under his control. It also explains why their decently conceived plan failed. Is it optimal, no but optimal is often bad writing. They had no reason to suspect that Orrin's defense would be strong enough to keep out all three of Sera, John and Kass. Other evidence for this is the color of the barrier around Orrin losing much of its green hue after Sera is caught.
But now that Sera is under his control, his own body is vulnerable. The next chapter or two is going to be John desperately trying to hold onto Sera in this brutal cage match, hopefully long enough for Kassandra and the others to break through and Hurt Orrin.