Wow, this was hard.
Adra and the dragons are well-known for their horrifying damage potential, and it's much worse without any equipment.
My team hasn't changed much, though I got two secret characters: Lini and Eldena. Secret characters can be good in this challenge because they already know two moves before they join you. Eldena is a very good unit, able to doublecast Barrier on the team. Lini can tank well with his Mog Guard skill, but there's not much use in Ultima Charge (which is just a bit stronger than a regular attack used by a White Monk).
Even with Shell & Protect applied, you can very easily die in two hits. The dragons engross, there's no space and everything is a mess. Awful situations are created every turn the enemy makes, i.e. being unable to heal an injured ally that's been surrounded or attack the boss for pretty much the same reasons.
I failed to beat this boss several times and was about to go powerlevel until I decided to do another attempt. Strangely, it worked.
It may not be noticeable in the considerably sped up video, but it was hard to decide what to do next and that's where all the hesitation comes from.
Strategy of proper unit placement reigns here, as do seemingly unimportant decisions and, of course, luck.
In the next battle I'll show how to deal with an enemy that has Reflex (a major pain in the backside).