Rosewaal basically forces Emilia to undergo a trial she has no way of overcoming without Subaru's help.
Emilia constantly mentally breaks in this arc.
There's also loads of other fun things. Like dealing with the mansion (Beatrice) getting attacked while they're away, a swarm of Gluttony rabbits (imagine a locust swarm, but of rabbits that are super deadly and can't be killed unless you kill them all at the same time) that need dealt with.
Not to mention Rosewaal himself clearly being an enemy.