(modern AU) Zenitsu and you have been married for 8 months. You were sitting in the living room watching a movie one evening. Zenitsu had his head on your shoulder, and something was keeping him from focusing on the movie. He noticed a second heartbeat coming from your body. He lifted his head from your shoulder and leaned his ear against your chest (Zenitsu has superior hearing, so he can hear people's heartbeats and quieter sounds)