here's a few ideas!!

linhardt/hubert - soulmate au "the one where only your soulmate can kill you."
lusamine/gangrel - kiss "kisses meant to distract the other person from whatever they were intently doing"
edelgard/lorenz - “I don’t say it often, but I do love you. Very much so.”
mondo/sayaka - “Let’s break the rules and take over the world.”