There is a possibility that his love interest could be a mermaid. In the world of pirates, mermaids are often a part of the lore. A mermaid who saves Zoro from drowning or some other danger, and then they fall in love, would make for an exciting love story.
In addition to Tashigi, in the vast world of fan theories, there could be other potential characters who might be Zoro's love interest. But these are mostly just unfounded speculations. The main and most prominent one that stands out is Tashigi because of the way their stories intersect with each other in the context of swords and their personal growth related to swordsmanship.
One day, Zoro got lost as usual on the ship. Nami found him and instead of scolding, she showed him the way with a smile. Since then, Zoro started to notice Nami more. Their relationship grew slowly as they fought side by side against enemies. Zoro would always protect Nami in battles, and Nami would patch up Zoro's wounds after. It was a quiet, budding love story.
Maybe it could be about Zoro falling in love with a strong - willed female pirate. They meet during a battle and gradually develop feelings for each other through mutual respect for their combat skills.
One way it could be developed is through shared adventures. They could be in a dangerous situation where Zoro's strength and Robin's intelligence work together to overcome the odds. For example, on an island full of ancient traps, Zoro defends them physically while Robin deciphers the clues to get them out. This mutual reliance could gradually turn into love as they start to respect and admire each other more deeply.
In many Ninjago fanfictions about Lloyd's love interest, it could be someone new created by the author. For example, a mysterious girl who has special powers and meets Lloyd during one of his adventures. They start off as strangers but gradually develop feelings for each other as they face challenges together.