Common themes in 'dark and Daisuke' yaoi fanfiction can be quite diverse. There could be a theme of sacrifice, where either Daisuke or the other character in the relationship has to sacrifice something important for the sake of the relationship or to deal with the 'dark' elements in the story. Another theme could be the exploration of taboos. Since it's 'dark' yaoi, it might touch on some topics that are considered taboo in normal relationships, like extreme possessiveness or a love - hate relationship that borders on the unhealthy. Additionally, the theme of transformation might be present, where Daisuke or the characters change as a result of the 'dark' experiences they go through in the story.
One common theme could be power dynamics. In a 'dark and Daisuke' yaoi fanfiction, there might be a situation where one character has more power over the other, creating an interesting and often tense relationship. Another theme could be internal struggle. Daisuke might be facing his own demons or moral dilemmas, especially in a 'dark' context.
Well, secrecy is often a theme. In yaoi fanfictions with 'dark and Daisuke', the relationship might be something that has to be kept hidden, either because of society's views or some other external factor. Also, redemption can be a theme. If Daisuke has made some 'dark' choices, the story could be about his journey to redeem himself within the relationship. And of course, love in the face of darkness is also a typical theme, showing how the relationship endures despite the difficult circumstances.