Zero no Tsukaima: Princesses no Rondo - Yuuwaku no Sunahama  

The Familiar of Zero: Rondo of the Princesses OVA, Zero no Tsukaima: Princess no Rondo OVA, Zero no Tsukaima: Princesses no Rondo Special, Zero no Tsukaima: Seductive Beach, Zero no Tsukaima: Episode 6.5, ゼロの使い魔 ～三美姫（プリンセッセ）の輪舞（ロンド）～ 誘惑の砂浜, The Familiar of Zero: "Rondo" of Princesses - Seductive Beach

DVD beach episode of Zero no Tsukaima: Princesses no Rondo. Also known as episode #6.5.