It does not need to be the protagonist . A sweet side couple in the story with hero and villain is ok too. It will be best if it's bl/yuri as i have read more story with hero x villain as het than bl/yuri. So i search more in the BL/GL genre but het is fine too. I'm biased toward villain so if it's villain (or reincarnate as a villain or time travel) it's the best but it's also fine if there a hero or og hero. If there romance all is fine for me.