If we are treating this as a game or LitRPG (Literary Role-Playing Game), the "best" Iris build cannot be a pure mage, rogue, or tank. The Labyrinth of Demons is designed to punish specialization.
Complete all character side-quests to unlock unique support skills. iris in the labyrinth of demons best
: A Giant's tear, which serves as the birthplace of her inner demons. If we are treating this as a game