Peachauline

Peachauline is the femslash ship between Pauline and Princess Peach from the Mario series.

Canon
Pauline was Mario's original love interest before Peach was introduced as her replacement since Super Mario Bros.

Both Pauline and Peach appear in the Puzzle "Nintendo Heroines/Starlets" alongside Rosalina, Zelda, and Toon Zelda. However, as the Puzzle can't be considered "canon" in the main Mario series, this mean that the two characters haven't directly interacted each other back then.

They finally met directly in Super Mario Odyssey and they're in good terms as they appeared together in the ending postcard. In the game they have some similarities: they're both authority figures, both were Mario's love interests, and while Peach is wearing a wedding dress, Pauline's mayor attire is a suit.

Fanon
Though Peach and Pauline respectively have older game appearances before Super Mario Odyssey, Peachauline actually is a quite new and well-received ship in the fanbase due to their similarities and both first time appear together in said game since Pauline was first revealed to be returning.

To this very day, Peachauline is a pretty popular Mario ship on Tumblr.