The first letter that Francis gets from an anonymous person with wild handwriting is simple, but it still makes him grin from ear to ear and hug the paper against his chest. Though, whether or not you could call these messages 'letters' is debatable. Really, they're just pieces of paper folded up with no name, address, or anything on them. Francis knows that they're for him, though. He just knows.

The first letter that Francis gets says,

Tes cheveux sont beaux.

Francis spends the rest of that day twirling his fingers through his hair.

—

The next letter that Francis gets comes a month later, and in the time period between the first letter and the second letter, Francis is almost afraid that the one letter he had recieved wasn't meant for him at all.

It is a very, very sunny day when Francis finds another piece of folded up paper with the same wild handwriting.

The second letter that Francis gets says,

Je t'aime beaucoup.

Later that day, his boss asks him why he's smiling so much. Francis just shakes his head a little and says, "Je suppose que je suis juste heureux aujourd'hui." Francis's boss looks a little skeptical, but he accepts this answer nonetheless.

—

The letters continue as simple one sentence messages of praise for three more letters before the messages start to become more complex.

The sixth letter that Francis gets says,

Tu es beau, tu es gentil, mais tu es pénible.

This one makes Francis smile and then frown. He doesn't know what to make of these mixed messages, and he walks around mildly confused all day. Something about how this letter comes across is also familiar, and though Francis has an idea about this familiarity, he strikes it down almost immediately.

—

Francis knows exactly who is sending him these letters when he receives the tenth one, which is even more complex than the past few letters.

Je suis un lapin; tu es une grenouille.
Je suis méchant, et tu es gentil.
Je te déteste, mais je t'aime à la fois.

Francis puts his bright red face in his hands and doesn't manage to regain his composure for a fair number of minutes. Arthur, Arthur, he says in his head, tu es si doux.

—

The next time Francis sees his secret admirer, his tiny hands are working themselves in knots, and he is looking everywhere but Francis's face. Francis immediately picks him up and gives him a crushing hug.

"Hey, ow! You're squeezing me too tight, frog!"

"Oh, Arthur! Merci beaucoup!" Francis peppers kisses all over Arthur's face, repeating the word 'merci' over and over. Arthur squeaks and pulls his arms up in front of his face.

"What on earth are you thanking me for?"

"As if you don't know." Arthur opens his mouth to argue, but he makes the mistake of looking into Francis's joy filled eyes. He lowers his arms.

"Okay, I did send you those letters…but don't tell anyone!" Francis gives Arthur one last kiss—directly on his forehead—before setting him down.

"I brought you a letter, lapin." Francis hands Arthur a folded up piece of paper.

This letter that Arthur gets says,

I love you, Arthur.

Francis can't help but to laugh at how red Arthur's face turns.

Years and years into the future, all of these letters will be carefully preserved, and Francis will never ever forget walking around filled with sunshine on the day when he got his very first letter from Arthur.

Translations:

Tes cheveux sont beaux - Your hair is pretty/beautiful

Je t'aime beaucoup - I like you a lot/I love you a lot (I was going for I like you a lot here but either way works)

Je suppose que je suis juste heureux aujourd'hui - I suppose that I'm just happy today

Tu es beau, tu es gentil, mais tu es pénible - You are pretty/handsome, you are nice, but you are annoying

Je suis un lapin; tu es une grenouille - I am a rabbit; you are a frog (grenouille is a feminine word, but purely feminine words in French don't accommodate for non feminine subjects, so I would use 'une' instead of 'un' [thank you Auto_Alchemechanicist over at ao3 for the tip!])

Je suis méchant, et tu es gentil - I am mean, and you are nice

Je te déteste, mais je t'aime à la fois - I hate you, but I like/love you at the same time (I was actually going for love here)

tu es si doux - you are so sweet

Merci [beaucoup] - Thank you [so much]