THE FINAL BATTLE
Attack!
Lopunny fires up her Ice Punch, her powerful legs launching her right up into the air before sending her frigid fist crashing down straight into Dragonite's big dopey face. He is, quite literally, out cold. Once the knockout blow is delivered, she turns right to you and ambushes you with a hug.
Your rival's still got four more available fighters, but that's less than you've got, so you take some pride in that. You're winning. You've never lost to her, no matter how close it got.
The Beast Ball she grabs from her belt makes you think that's bound to change.
As Dragonite's replacement, your rival sends out one of the Ultra Beasts, an alien Pokemon from another dimension and the very thing that led to you obtaining Lunala in the first place. Before you stands the Bug/Fighting Pheromosa, one of the most difficult fights you've had to battle in your time adventuring. She is way too strong and way too fast to deal with properly, and her Beast Boost ability makes her FASTER every time she KO's an opponent.
Lopunny can't match Pheromosa's BASE speed, and she's horribly vulnerable to Fighting-type attacks. Swapping out will only waste your turn and get whoever you send out taken down immediately. Even if they survive the first hit, they won't outpace the second, and each successive failure to deal with her will only make her harder to deal with.
You need Lopunny to faint so that Lunala can switch in without taking up your turn AND stay up long enough to take Pheromosa out. Lopunny seems to understand; she looks upset, but she trusts you. She gives you another hug before turning to face Pheromosa, ready to take the fall so you can take the win.