That stage has been difficult for some people in the past too, but has been repeatedly and heavily nerfed to be much easier. You should be able to clear it easily with a team with characters like Maria, Valerie, Laura, Camila, Tio and whoever else you may like. You just need strong DPS characters and you're good.
It is indeed hard to do it with this team, though I did it after a few manual tries, just focusing the demonlings with the melee units while the others focus on the nun, then start going after Xazariel.
For the easiest clear I recommend you just pull maria and make her level 40.
Also as I see you are commenting on the 1.1.5 version post? The enemies in the stage as a whole were quite heavily nerfed in 1.2.0, so if you are on the older version you should try the update.
You have a counter until you hit the next Hyper character above the recruit button. If you want to get specifically her, then recruit on the second banner by pressing the arrow on the right of the screen when you open the recruitment menu.
As for a combo, you can use Tio + Vionne, as thats quite a strong one. Another character that might be useful is Irina as she can target the Nun. If you pulled Nady instead of Maria, she is quite strong too, so you can also use her too.