For defense, Black Knight definitely at left flank. Honestly, I would move Arthur to Right Flank and your sniper, Poseidon, to Right Wing because snipers do better on the wings. You’ll typically see your single-target sharpshooters like Lianna, Marjana, Magni, or Joon on the wings. Do you have a good Seshat or Sartana to toss in at Left Wing? Edit: Nevermind. I just realized you said you didn’t have a 5-star Dark. Do you have a Proteus you can ascend and place in Left Wing? Hs will be ideal defensively, if you don’t have a 5* Dark. And once you level BK, I’d consider turning my attention to Mitsuko and place her at Right Wing and Poseidon in Left Wing. If someone tries to stack Ice on you to eliminate BK or Mitsu, they run the risk of running into Mitsu’s Ice reflect. Then, you still have Telluria healing with meat shields.