Gatekeeper Paralogue(not really): Eagles, Lions, and Deer
I got jebaited. This one doesn't have you playing the Gatekeeper, it's actually a Shez solo. It still requires you to have Gatekeeper, who joins early in your 3rd playthrough.
It's much easier than the Arval Paralogue for a couple of reasons: First, by the time you unlock Gatekeeper you've been working on Shez for 2 entire playthroughs, so they should be quite powerful by now. Second, there's a bunch of refill items so even if you spam Swift Slice, you don't really need to worry about running of of weapon durability.
Still, like any solo mission, the Damage Taken requirement isn't trivial. Watch for the 3 Lords getting red aura while fighting you. At which point you'll want to use the i-frames from Combat Arts and Specials to take them on safely!
0:00 Pre-mission cutscene
2:19 Unit Stats
3:09 Mission Start
13:10 Results
13:43 Post-mission Cutscene