This is the first two-for-the-price-of-one day. There will be others.
Probably Marius/Cosette from the musical version of Les Miserables, which is really weird because Eponine was far and away my favorite character. It just never occurred to me to question that Marius/Cosette was the OTP, and I loved Cosette too. To be more precise, most likely I wanted to be Cosette, and I was completely infatuated with Eponine. Her unrequited love just made her more desirably tragic to my seven-year-old-self. Really, I loved Les Miserables a lot when I was in elementary school, before I could understand half of it, and that included the pairings.
Yes, I did read the book. Sort of. I skipped huge chunks of Victor Hugo's meandering, but I read the plot-relevant bits. I may have been ten at the time.
If you want to go even earlier, there's Aurora/Prince Phillip from Disney's Sleeping Beauty, but since my investment in that was mostly "squee Aurora!" I'm not sure if it counts. I did later (much, much later) look up Perrault's version of the story and find Sleeping Beauty's meeting with the Prince utterly charming in that version (no, that was not one of the versions with rape, thankfully), so I guess I still ship some variant of that.
Day 02 - What was your very first ship?
Day 03 - A pairing that needs to happen now?
Day 04 - The pairing with the most chemistry?
Day 05 - The pairing with the least chemistry?
Day 06 - The best kiss?
Day 07 - The most heartbreaking scene?
Day 08 - The pairing with the most baggage?
Day 09 - The most believable relationship?
Day 10 - Why aren't these two married in real life?
Day 11 - What is your dream pairing?
Day 12 - Who had the best wedding?
Day 13 - What is your favorite television pairing?
Day 14 - What is your favorite book pairing?
Day 15 - What is your favorite real life pairing?
Day 16 - What is the absolute worst pairing?
Day 17 - A pairing you thought would never work out, but did?
Day 18 - What is the cutest pairing?
Day 19 - A pairing you've rooted for since the beginning?
Day 20 - The "can't stand the sexual tension anymore" pairing?
Day 21 - A pairing you like and no one else understands why?
Day 22 - A pairing you hate and no one else understands why?
Day 23 - A crazy love triangle/quadrilateral that worked out great?
Day 24 - A crazy love triangle/quadrilateral that worked out badly?
Day 25 - A pairing that was/would-be adorable, but could never work out?
Day 26 - A pairing that you hated and ended up loving?
Day 27 - A pairing that you loved and ended up hating?
Day 28 - A pairing that you will never understand?
Day 29 - What ship had the best proposal?
Day 30 - Your favorite ship forever and ever and ever?