Thanks
Waxer, Aleyo, Fulminato and Drakan47.
This fight almost filtered me from the game, so here goes a more detailed strategy for future reference (i know that works besides the stunning chances and other factors because i tried it two times with victory):
1st turn:
-Robin´s DISRUPT the Erosian REAPER
-Riala´s FIRES OF LUST all enemies
-Qm´s Arousing Aura all allies
-Vhala´s Defensive Rain all enemies
2dt turn:
-Robin´s DISRUPT the Erosian CAPTAIN
-Riala´s FIRES OF LUST all enemies
-Qm´s healing kisses however took the blunt of damage
-Vhala´s Offensive Rain all enemies
3rt turn:
-Robin´s DISRUPT the Erosian HEALER
-Riala´s FIRES OF LUST all enemies
-Qm´s healing kisses however took the blunt of damage
-Vhala´s Arrow of Abstninence on that damn Erosian Succubus, luckily to strike her out
If you survived the 3 first turns, rince and repeat Riala´s all-enemies attacks and keep disrupting the healer, the reaper and the captain. Vhala´s NEEDS to dispatch that motherfucking succubus, or else. If you did, Defensive rain the shit out of them every turn - don´t forget to keep Disrupting the Reaper, the Captain and the healer or you´re toast.
... i also think it would be way funnier (and less infuriating) if there´s an event, option or even an item with an 'analysis' option linked to annoying boss fights like these, to give the player those tips before a rough fight, for looking for those on the internet usually spoils the story.