The boss of Cafe Leblanc is Shadow Sae, a formidable opponent with a gambling motif. Shadow Sae has no inherent weaknesses but is resistant to several physical attacks. She primarily uses Almighty attacks, Fire, and Ice skills. Her signature move is 'Roulette', where she spins a wheel that can inflict various status ailments on your party or deal massive damage. The outcome of Roulette is somewhat random, but certain actions can influence it.
Shadow Sae will occasionally summon 'Shadow Guards' minions. These minions are weak to Electric and Wind. Prioritize taking them out quickly to prevent them from supporting Shadow Sae and to gain Boosts for your party. She can inflict 'Despair' and 'Fear' status ailments, which can be particularly debilitating. Have items or skills to cure these (e.g., Amrita Soda, Patra). Focus on consistent damage, maintaining buffs/debuffs, and managing status ailments. When she uses 'Roulette', try to have your party's HP high and be ready to heal or cure status effects. This is a battle of endurance and luck, so be prepared for a long fight.