Rosa Diaz and Marcus first meet when Marcus comes in to see his uncle, Captain Holt. They are instantly attracted to each other and begin a relationship. They break up in Into the Woods although Rosa still had feelings for him.
- Rosa and Marcus meet and Rosa says goodbye (Which Gina says is the equivalent of her going and jamming her tongue down his throat)
- Marcus asks if Rosa is single via Holt.
- Rosa says that Marcus has to ask for her number personally if he wants it.
- Rosa and Marcus sleep together and Rosa awkwardly walks in whilst Kevin and Raymond are eating.
- Rosa breaks things off with Marcus.
- Holt tells Rosa that it is okay if she wants to be with Marcus and they begin a relationship.
- Marcus gets Rosa a phone charger and kisses her goodbye.
- Marcus and Rosa text romatically.
- Rosa doesn't invite Marcus to the wedding.
- Rosa realises she is being a coward and invites Marcus.
- Rosa and Marcus kiss and say they love each other.
- Rosa and Marcus have dinner with Captain Holt and Kevin. Marcus is at ease but Rose feels uneasy.
- Rosa reveals she might be pregnant with Marcus's baby but it is a false alarm.
- Marcus rents out an entire bar for Rosa's birthday, so they can spend it together.
- Marcus is the sole attender at Rosa's birthday party which she likes.
- Rosa decides to break up with Marcus as he is very emotional.
- Rosa breaks up with Marcus and Marcus gets upset.
- Rosa admits that she still cares for Marcus but he wanted to get married and she didn't.
- Rosa wonders if she has messed up her one chance at love and cries.
‘I love u’
- Marcus is Rosa's first on screen love interest (She mentions having a boyfriend prior to their meeting).