This question involves many common plots and settings in online novels. The following is my understanding and answer: The reason why the security guard was charming was probably because he had a unique personality and characteristics under his ordinary appearance. He may be smart, reliable, brave, and caring, all qualities that make him a person worthy of dependence and respect. Security guards might show extraordinary abilities in certain aspects. For example, he might have special skills or professional knowledge that might leave a deep impression on the beauty. Or he might show a sense of humor or wit on certain occasions to make a good impression on the beauty. Beautiful women might develop feelings for security guards for certain reasons. Perhaps it was because she needed his help at work or because he showed some special attention and care to her, which made her feel good. The charm of the security guard might come from his ordinariness and authenticity. This authenticity might make the beauty feel that he was closer to the person she wanted. In addition, the security guard's ordinariness and authenticity may also make him a person who can be trusted and relied on. This may give the beauty a sense of security and trust, thus deepening her feelings for him.