Often, intense emotions are a common element. The passion between the characters is so strong that it might be considered dangerous. Another element could be secrecy. Maybe the relationship is forbidden in some way, like in a society where certain relationships are not allowed.
One common element is conflict. Since it's a 'dangerous passion', there has to be something that makes this passion risky. It could be external forces like rivalries or different loyalties. For example, if it's a fanfic about two characters from warring factions, their love would be dangerous. Also, internal conflict within the characters themselves is common. They might struggle with their own feelings, whether to give in to this dangerous passion or resist it.
In 'a dangerous passion fanfic', there are usually high - stakes situations. The passion isn't just a simple love story. It might involve life - and - death situations. The characters' passion could put their lives, reputations, or the well - being of others at risk. There's also a sense of allure. The danger itself makes the passion more exciting and alluring, like a moth to a flame. This allure is what draws the characters together despite the risks.