Teal hair and Cerulean flowers (Wedding gone wrong!)

Hatsune Miku is about to get married to her fiance, Vriska Serket! What could possibly go wrong? What does Sans (future father-in-law) mean by "watch out for cat girls?"

OR

Me when I am to get married to a possibly immortal troll god spider girl but a cat girl interrupts and reveals my future wife is a cheater so I run to my best friend's house (who is in love with me).