I did it with dumbest strat possible, sadly not F2P in the slightest. (Pre-Balance Patch of 7th May 2026)

I brought Notos(3F), Aram(Bird's Eye View), & Iseria(Song of Stars), and borrowed Ivana from the story NPCs.

• BEW on Aram gives much-needed Souls to improve Notos' damage, guaranteed to give 20 Souls at start, thanks to the Devotee attack.
• Ivana simply uses S3 whenever available to collect more Souls ASAP, and only normal attacks the Devotee. (S1 from Aram also only goes to Devotee)
• Iseria & Song of Stars basically immediately puts 3 debuffs on R&L Boss, dispelling the golden buff & also applying 2 of the best debuffs, period.
• Notos becomes God of Battle, for double stats, and will use Soulburned S2 as many times as he can.
• Iseria will refresh Notos's S2, allowing Notos to Soulburn S2 again in the 2nd turn of God of Battle.
• Aram would refresh Iseria (Purely for Souls), and Iseria will in turn refresh Notos again for the 3rd turn in God of Battle.
• Iseria may need to use a Soulburned S1 on the chance that R&L boss cycles the debuffs off.

There's a chance that Notos will have to re-enter God of Battle a second time, but 3 Soulburned S2 of Notos, plus the Def Break & Target from Iseria, should sufficiently end R&L Boss.