The Blue Noel team is safe for Legendary (if there are no fire demons on stage 4) until Valkyrie gets low on hp and starts spamming Valkyrie Blade, but it is really slow so I switched to another team.
Leader: Blizzard Archdemon Amon Lv 56
Awoken Hera-Is Lv 60
Awoken Hera Lv 92
Awoken Hera Lv 68
Siren the Enchanter Lv 70 - max skilled
Friend: SOD Lucifer max lvl
Team has 36,000 hp and almost 6,000 rcv. Amon gives 1.5x to hp/atk/rcv for devils. It was much faster but still did not get the drop.
Stage 1 - devils, fine if you get good orb drops
Stage 2 - masks, kill mystic mask first
Stage 3 - dark golem, triple gravity and Amon's skill, and then grind down and charge gravities
Stage 4 - demons, double gravity and use Lucifer to kill one (kill fire demon first) and then grind and charge
Stage 5 - Valkyrie, use 1 gravity immediately and then Amon after her shield and you will get 5 counterattacks, survive 30 turns to charge up the gravity you used and then triple gravity and Lucifer to kill her before she starts using Valkyrie blade.