I love clerith because I love the positive effect Aerith has on Cloud. She works to bring out the best in him with patience and gentleness—she knows he is fragile, even if he tries not to show it, and she tries as hard as she can to make him smile, because his happiness is hers.

AC I think is the perfect example of Aerith’s influence on Cloud.
Others in Cloud’s life are frustrated with him because he’s ill, depressed, and has given up on life.
Meanwhile, Aerith is patient and encouraging.

“You came, even though you’re about to break. That’s a good sign.”
Aerith acknowledges that Cloud is at the breaking point, and she gives him positive reinforcement to keep him going down the right path, so he knows that even if it’s painful, it’s good that he’s doing this.

Aerith is never harsh or impatient with Cloud. And he confides in her what he’s truly feeling, feelings that he won’t share with anyone else, because she is able to bring out that vulnerable side of him. He feels comfortable being open about his pain with her.

Aerith probably already knew how Cloud felt but still, she’s gentle and patient. She assures him that she never blamed him, and tells him that he needs to forgive himself.
She’s never frustrated, she doesn’t expect him to already know and get angry when he doesn’t act right.

She sees that he’s going down the wrong path, so she gently nudges him the right way with nothing but love. How she treats him brings out the best in him. And even at the very end, she continues to assure and encourage him so he will smile.
“See? Everything’s alright.”