To write a good 'Star Wars OC Lemon Fanfiction' without crossing the line, it's essential to respect the source material. Your OC should fit into the Star Wars world seamlessly. As for the 'lemon' part, think of it as a way to add depth to the relationships in your story. You can use euphemisms and innuendos to suggest a more intimate connection. But don't overdo it. Maybe your OC has a secret crush on a Jedi Knight. You can show their admiration and the tension between them in a more subtle way, rather than writing something inappropriate. This way, you can create an engaging story that still adheres to the general ethics of fanfiction writing.