Hidden Truths 1 (見えざる史実 • 前 Miezaru Shijitsu - Mae lit. Invisible Historical Fact - Previous in the Japanese version) is Xenologue 7 of Fire Emblem Fates.
You'll want to focus on keeping the three close together to help them assist each other in a fight, some units will drop stat upgrades, which should be given to one unit who will be essentially leading the fight. Severa can make a good leader, because she has the highest Defense and Strength of the three. You can pair Inigo with her, and have Owain use the Levin Sword as ranged support. Keep all three close together often, and remember to be easy on the Concoctions. Also, make sure you give the stat boosters to whoever needs them the most. For example, Owain should use the Dracoshield and Inigo should use the Talisman. You'll need all three units when you fight the Swordmaster boss in the end, though he can be beaten otherwise with slight difficulty.
The script for this Xenologue can be found here
Fell Brand (After Completion)
Because Owain uses the exact same voice samples as his Odin persona instead of his Awakening lines, he may prematurely refer to himself as "Odin Dark" upon executing a Dual Guard.