In my 0%-growths HM run, I planned out a two-turn clear of Chapter 12 requiring two Captured Pegasus Knights (only one is required if the Mess Hall is allowed); Haitaka with two level-ups gained in Chapter 10 (for Swap); promoted Kaze at base for his +5 Spd Pair Up (not required if the Mess Hall is allowed); and Corrin with a Dragon Talent, promoted to a Wyvern Lord, with a C Support with Camilla from grinding in Chapter 10. None of this should require a particularly great real-time investment if visiting other Castles for foodstuffs with which to recruit Prisoners, and should be possible in a continuous LTC playthrough, with or without growths.
(disclosure: I had trouble soft-patching my game with my 0%-growths patch a while ago because of a recent firmware update and so never tested the two-turn clear in full; I'll understand if you don't believe my description of the clear.)
With a Kaze Pair Up, one of the Pegs can start in range of the +4 Def pot and receive the boost before flying to break the center-left pot with a Javelin. With the +4 Def on the Peg, the two Samurai should be manipulated into attacking Peri (this I have NOT tested), who OHKOs in Attack Stance (with the Peg) thanks to a Bloodthirst boost from KOing the Ninja below the center pots during PP1.
I'll not describe the Sheltering logistics since my memory is hazy. Jakob, Peri, and Silas should all have it, though I don't remember if they all need to use it during PP1.
Camilla Pairs with Corrin on PP1 and gets Swapped by Haitaka before Switching, Lunging and OHKOing with a Hand Axe Enemy 28 in this link. In Attack Stance with Peri, Beruka can Lunge and OHKO Enemy 30.
This clear assumes that you manipulate Saizo into attacking Beruka from the center-left forest tile; as I pointed out earlier, I tested this particular manipulation in a file with growths back when I was still interested in finishing my 0%-growths playthrough. It has been a while since I played the game, so I might be wrong on this, but I don't think this manipulation is strictly necessary for a two-turn clear of this Chapter, and that it's required only for obtaining the Flame Shuriken.
During PP2, the Peg Knight carrying Kaze files onto the Dragon Vein and Transfers Kaze to Camilla in exchange for Corrin, who triggers the Dragon Vein. Camilla moves with Kaze. Azura must be ferried over to Beruka, who in turn flies with her max Mov to let Azura Sing for Camilla, who can ORKO the weakened Ryoma with a Spd Tonic, Str Tonic, and either Mess Hall usage or a Rally from Laslow's Personal Skill. Don't forget to grab the Flame Shuriken before the bosskill.
I (and a handful of others) don't play this form of LTC absolutism precisely because it is so time-inefficient. If the concept of LTC comes from wanting to be efficient (in the everyday sense), then a clear requiring a great deal of time to execute, even after it has been conceived of, is not compatible with the concept of efficiency to me.
I won't knock anyone who plays this way, though; I enjoyed the video.