The Short Answer
Ruinous Oath is a late-game collection unlock. Reach level 750, save 5,000,000 C$, and complete the entire Crimson Cavern Bestiary in both Shiny and Sparkling forms. When every requirement is complete, buy it from the pedestal beside the Crimson King.
Do Not Confuse Normal Completion With the Real Gate
A normal caught marker is not enough. The requirement is full Shiny and Sparkling coverage for the Crimson Cavern collection. Audit the rows separately: one missing Shiny marker or one missing Sparkling marker can keep the rod locked even when the ordinary Bestiary looks complete.
Prepare the Level and Currency Gates
- Reach level 750 before treating the rod as an immediate target.
- Keep 5,000,000 C$ available at the August 25, 2026 price.
- Finish Crimson Cavern access and confirm every required row has both special markers.
- Return to the pedestal beside the Crimson King and verify the live prompt.
Why the Grind Is So Long
The rod is positioned as an upgrade to the Luminescent-style play pattern, not a universal shortcut. High luck, lure speed, unlimited weight, and strong progress effects reward the work, but the catch still asks for consistent execution. The expensive part is the collection state, not only the listed cash price.
Troubleshoot a Locked Pedestal
If the purchase remains locked, check level, cash, cavern access, Shiny coverage, and Sparkling coverage in that order. Do not assume a visual percentage proves both variant sets are complete. If your live requirement differs after a major update, trust the current in-game prompt and treat this August 25 snapshot as history, then revisit the next-rod guide before committing more grind time.