Any of these can be M rated.

• Annabeth notices Piper constantly writing in a journal. When Piper accidentally leaves it in the Athena cabin after hanging out with Annabeth, Annabeth might’ve taken a peek and seen that Piper has written about her feelings for Annabeth. There are also doodles of their names combined. Flustered and embarrassed Piper.
• Piper and Annabeth’s first time. Piper is inexperienced and shy. Annabeth is confident and forward.
• Annabeth has had a feeling that Piper likes her. Piper then comes out to her.
• During the Cupid debacle, Piper has her feelings for Annabeth revealed. Annabeth is there to witness it. Piper is embarrassed and once the spell is over she runs away, but Annabeth is faster.
• Annabeth and Piper are roommates and then they’re forced to stay inside because of the pandemic. Feelings come out.
• Piper tried telling Annabeth she likes her, but things keep preventing her from doing so. She finally gets the chance to tell her and then kisses her and runs away.
• Piper is in love with Annabeth, but Annabeth is dating Percy, or is she? Annabeth has noticed Piper is jealous, but thinks it’s because she’s jealous of the relationship she lost with Jason. How wrong she is.
• Piper has nightmares and only Annabeth can help her. Feelings come out.
• After the Temple of Fear debacle in BoO, Piper realizes she loves Annabeth as more than just a friend. But does Annabeth feel the same way?
• Piper tells Leo and Nico about her crush on Annabeth and Annabeth overhears.
• Piper hears Annabeth talking to Percy about a crush and Piper thinks Annabeth is talking about another boy. But she’s talking about Piper.
• Piper and Jason break up when they realize that while they love each other, they aren’t in love with each other. Piper now realizes she’s in love with Annabeth. She confides in Jason who says maybe Annabeth loves her too. Only thing is, Annabeth and Percy are still in a happy relationship.
• Piper thinks Annabeth is dating Thalia and is very jealous.
• Thalia encourages Piper to confess her feelings to Annabeth