INFERNO CLIMBER: REBORN - Getting the Dragon King Sword

Thanks to help from ‪@ShadowKisuragi002‬ I was able to figure out what was going wrong with getting the sword. I believe based on my experience that you NEED to use the Demonic Greatshield to get the Dragon King Sword. After spending multiple attempts using the Dark Iron Greatshield with no luck, I've used the Demonic Greatshield and it's worked both times.
Also, the 4 gems are Deflect Plus Plus.