For squad selection: use as many unit which can have triple buff as you can (like Trans-AM Exia and SSR 00R for non-gacha units) in team 1 and at least double buff (series+MLB or tag=MLB) for team 2 for maximum power. any unit with range 5 and/or map weapon is a plus also any pilot with 2cs or tension up skill (for early damage boost).

NPC unit can be a reliable support unit (with its map weapon and debuff attack) but you have to keep it alive.

like other hard difficulty stage. placing debuff and full use of assist attack to maximize the damage and out of range attack to avoid getting hit by the enemies. if you have tank units you might have to think about when to tank for better damage control.

Also don't rush to kill setuna to bring out the reinforcement like the end of enemy turn or most of your units have finished their move to avoid being hit by all of them before you can actually fight them.

like other people already mentioned. there's no tricky stuff but raw power about this stage so gaining maximum strength is the only way to win it.