Sanji, a character from the popular manga and anime One Piece, was left behind by Zoro during a battle due to a misunderstanding. The concise answer to "Where is Sanji?" is that he was separated from the rest of the Straw Hat Pirates during a fierce battle with the World Government's navy. As for "Why didn't Zoro Save Him," the reason is that Zoro believed Sanji was safe with the others, as he had seen Sanji leave the battle area moments before.

In the second paragraph, the explanation delves into the context of the situation. During the battle, Zoro was engaged in a fierce duel with a high-ranking naval officer, Akainu. Amidst the chaos, Sanji, who had been injured, decided to leave the battlefield to seek medical attention. However, Zoro, focused on his own battle, did not notice Sanji's departure. According to the manga, Zoro's perception was clouded by the intensity of the fight, and he did not realize that Sanji had left the scene. This misunderstanding was compounded by the fact that Sanji did not want to burden Zoro with his injury, so he did not call out for help.

Data from the manga series supports this analysis. In the One Piece manga, it is clear that Zoro is known for his unwavering focus and determination in battle. This single-mindedness often leads to him being oblivious to his surroundings, as seen in various instances throughout the series. Additionally, Sanji's character is known for his bravery and selflessness, which is evident in his decision to leave the battlefield to seek help without causing alarm to his companions.

The incident with Sanji and Zoro serves as a poignant example of the dynamics within the Straw Hat Pirates. It highlights the trust and camaraderie among the crew, as well as the individual strengths and weaknesses of each member. Zoro's dedication to his battle and Sanji's willingness to sacrifice for the group are central themes in the series, contributing to the rich tapestry of the story.