Ciel, Merlin and Koyan of Light with Atlas MC. You need Poster Girl on Ciel and her Append25 at lvl 6 minimum (for skill 2 and 3) if you want to do enough damage to clear in 2 turns. Alternatively, if you have lvl 120 Ciel, maybe you can make use of alternative CEs like Sumo and not feel too bad about the loss. The gameplan is to use all buffs on Ciel then BNPB with the first target being the left-most golem on Wave 1. That way, you'll crit kill it then NP the right-most golem and finally crit-kill the 1m HP golem. Wave 2 is using Atlas CDR onto Ciel then rebuff Skill 2 and 3 and NPBB the boss. You should kill it in one turn.
This setup is a bit scuffed since you only have 20 stars and any stars not going into the two Busters make it inconsistent and may require way more than 3 turns. An alternative solution is to give up another CE slot to run a 20 star bomb CE so you're guaranteed the clear. Another alternative solution is to have a grailed Ciel. I managed to reduce the maximum turn clear to 3 turns by having my Ciel have enough ATK such that I can use Buster 1st on the 1m HP golem instead, drastically reducing the impact of crit reliability (not completely but I haven't seen it to be a problem yet). My Ciel was lvl 100 and I think 1600 Atk Fou? I could be wrong on what threshold you need to meet.
EDIT: I wrote Append 2 but I meant Append 5. My bad.