Sozen So according to Fulminato, the dark swirls work on a point system that increases as quests are done and decreased with treatment. To quote him:
"Aka Deprivation:
Deprivation Score 4-: "2 Dot" [-5% MaxHp/Round]
Deprivation Score 5-9: "3 Dot" [-10% MaxHp/Round]
Deprivation Score 10+: "4 Dot" [-20% MaxHp/Round]
Deprivation Score:
Start: 10
Initial Burst from Robin: Score -1
"Tentacle" Ritual: Score -3
"painful" Ritual: Score -6
Jade Sabotage 4+: Score +1 [when robin tell you had done enough to weaken house jade]
Resolve Mine Problem: Score +1 [any solution]
Jade House & Jade Sabotage 3- & Trin Capped: Score +1 [replace +1 for Jade Sabotage]
Talk with Lade Rose: Score +1
Resolve Elf Problem: Score +1 [Any Solution]
Win Each Fight in the Pits: Score +1 [+3 aftet all the fights]
Complete All Order Trials: Score +1"
So the number of swirls depends on the order that events are done. If aka's condition is done early, the swirls will drop to 2 before going back up to 3 as more quests are done. If several quests are done first, the swirls increase to 4 and the aka's condition quest treatments will drop it back to 3.